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THE 

MECHANISTIC  CONCEPTION 

OF  LIFE 


THE  UNIVERSITY  OF  CHICAGO  PRESS 
CHICAGO,  ILLINOIS 


Bgents 
THE  BAKER  &  TAYLOR  COMPANY 

NEW    YORK 

THE  CAMBRIDGE  UNIVERSITY  PRESS 

LONDON  AND  EDINBUBOH 


THE 
MECHANISTIC    CONCEPTION 

OF  LIFE 


BIOLOGICAL    ESSAYS 


BY 


JACQUES  JX>EB,  M.D.,  PH.D.,  SO.D. 

MEMBEB  OF  THE  KOCKEFELLEE  INSTITUTE 
FOE  MEDICAL  EESEAKCH 


THE  UNIVERSITY  OF  CHICAGO  PRESS 
CHICAGO,  ILLINOIS 


3m 


^T 
1^(;l 


Copyright  1912  By 
The  University  of  Chicago 


All  rights  reserved 
Published  July  1912 


317102 


BOSTON  COLLEGE  LIBRARY 
CHESTNUT  HILL.  MASa 


DEC  7     19Si 


Composed  and  Printed  By 

The  University  of  Chicago  Press 

Chicago,  Illinois,  U.S.A. 


BOSTON  COLLEGE  LIBRARY 

CHESTNUT  HILL,  MA 021 67 

JAN  3  ^  ^289 


PREFACE 

The  essays  contained  in  this  volume  were  written  on  differ- 
ent occasions  mostly  in  response  to  requests  for  a  popular 
presentation  of  the  results  of  the  author's  investigations.  The 
title  of  the  volume  characterizes  their  general  tendency  as  an 
attempt  to  analyze  life  from  a  purely  physico-chemical  view- 
point. Since  they  deal  to  a  large  extent  with  the  personal 
work  of  the  author,  repetition  was  unavoidable,  but  in  view  of 
the  technical  difficulties  presented  by  some  of  the  topics  this 
may  serve  to  facilitate  the  understanding  of  the  subject. 

The  author  wishes  to  thank  the  editors  and  publishers  who 
gave  their  consent  to  the  reprinting  of  these  essays :  Professor 
J.  McKeen  Cattell,  of  Columbia  University,  Professor  Albert 
Charles  Seward,  of  the  University  of  Cambridge,  England, 
Ginn  &  Co.,  of  Boston,  G.  P.  Putnam's  Sons,  of  New  York  and 
London,  and  the  J.  B.  Lippincott  Company,  Philadelphia. 

The  Rockefeller  Institute 

FOR  Medical  Research 

April  4,  1912 


TABLE  OF  CONTENTS 

PAGE 

I.   The  Mechanistic  Conception  of  Life        -        -        -        -        3 
11.  The  Significance  of  Tropisms  for  Psychology  -        -      35 

III.  Some  Fundamental  Facts  and  Conceptions  concerning  the 
Comparative  Physiology  of  the   Central   Nervous  Sys- 
tem    ----------65 

IV.  Pattern  Adaptation  of  Fishes  and  the  Mechanism  of 

Vision  -------._      79 

V.  On  Some  Facts  and  Principles  of  Physiological  Morphol- 
ogy-         --85 

VI.   On  the  Nature  of  the  Process  of  Fertihzation  -        -     113 

VII.   On  the  Nature  of  Formative  Stimulation  (Artificial  Par- 
thenogenesis)      -        -        -        -        -        -        -        -127 

VIII.   The  Prevention  of  the  Death  of  the  Egg  through  the  Act 

of  Fertilization  _______     155 

IX.   The  Role  of  Salts  in  the  Preservation  of  Life  -        -        -     169 

X.   Experimental  Study  of  the  Influence  of  Environment  on 

Animals       ---------     195 

Index       -----------    229 


I.     THE  MECHANISTIC  CONCEPTION  OF  LIFE 


THE  MECHANISTIC  CONCEPTION  OF  LIFE^ 

I.      INTRODUCTORY 

It  is  the  object  of  this  paper  to  discuss  the  question 
whether  our  present  knowledge  gives  us  any  hope  that 
ultimately  life,  i.e.,  the  sum  of  all  life  phenomena,  can  be 
unequivocally  explained  in  physico-chemical  terms.  If  on 
the  basis  of  a  serious  survey  this  question  can  be  answered 
in  the  affirmative  our  social  and  ethical  life  will  have  to  be 
put  on  a  scientific  basis  and  our  rules  of  conduct  must 
be  brought  into  harmony  with  the  results  of  scientific 
biology. 

It  is  seemingly  often  taken  for  granted  by  laymen  that 
*'truth",ijL-bioLogy,  or  science  in  general,  is  of  the  same  order 
as  '^truth"  in  certain  of  the  mental  sciences;  that  is  to  say, 
that  everything  Tests  oh  argument  or  rhetoric  and  that  what 
is  regarded  as  true  today  may  be  expected  with  some  proba- 
bility to  be  considered  untrue  tomorrow.  It  happens  in  sci- 
ence, especially  in  the  descriptive  sciences  like  paleontology  or 
zoology,  that  hypotheses  are  forwarded,  discussed,  and  then 
abandoned.  It  should,  however,  be  remembered  that  modern 
biology  is  fundamentally  an  experimental  and  not  a  descrip- 
tive science;  and  that  its  results  are  not  rhetorical,  but  always 
assume  one  of  two  forms:  it  is  either  possible  to  control  a 
life  phenomenon  to  such  an  extent  that  we  can  produce  it  at 
desire  (as,  e.g.,  the  contraction  of  an  excised  muscle);  or  we 
succeed  in  finding  the  numerical  relation  between  the  con- 
ditions  of  the   experiment   and   the  biological  result   (e.g., 

1  Address  delivered  at  the  First  International  Congress  of  Monists  at  Ham- 
burg, September  10,  1911;  reprinted  from  Popular  Science  Monthly,  January, 
1912,  by  coxirtesy  of  Professor  J.  McKeen  CatteU. 

3 


4  The   Mechanistic  Conception  of  Life 

Mendel's  law  of  heredity).     Biology  as  far  as  it  is  based  on 
these  two  principles  cannot  retrogress,  but  must  advance. 

II.      THE    BEGINNING    OF    SCIENTIFIC    BIOLOGY 

Scientific  biology,  defined  in  this  sense,  begins  with  the 
attempt  made  by  Lavoisier  and  Laplace  (1780)  to  show 
that  the  quantity  of  heat  which  is  formed  in  the  body  of  a 
warm-blooded  animal  is  equal  to  that  formed  in  a  candle, 
provided  that  the  quantities  of  carbon  dioxide  formed  in  both 
cases  are  identical.  This  was  the  first  attempt  to  reduce 
a  life  phenomenon,  namely,  the  formation  of  animal  heat, 
completely  to  physico-chemical  terms.  What  these  two 
investigators  began  with  primitive  means  has  been  completed 
by  more  recent  investigators — Pettenkof er  and  Voit,  Rubner, 
Zuntz  and  Atwater.  The  oxidation  of  a  food-stuff  always 
furnishes  the  same  amount  of  heat,  no  matter  whether  it 
takes  place  in  the  living  body  or  outside. 

These  investigations  left  a  gap.  The  substances  which 
undergo  oxidations  in  the  animal  body — starch,  fat,  and 
proteins — are  substances  which  at  ordinary  temperature  are 
not  easily  oxidized.  They  require  the  temperature  of  the 
flame  in  order  to  undergo  rapid  oxidation  through  the  oxygen 
of  the  air.  This  discrepancy  between  the  oxidations  in  the 
living  body  and  those  in  the  laboratory  manifests  itself  also 
in  other  chemical  processes,  e.g.,  digestion  or  hydrolytic 
reactions,  which  were  at  first  found  to  occur  outside  the 
living  body  rapidly  only  under  conditions  incompatible  with 
life.  This  discrepancy  was  done  away  with  by  the  physical 
chemists,  who  demonstrated  that  the  same  acceleration  of 
chemical  reactions  which  is  brought  about  by  a  high  tempera- 
ture can  also  be  accomplished  at  a  low  temperature  with  the 
aid  of  certain  specific  substances,  the  so-called  catalyzers. 
This  progress  is  connected  pre-eminently  with  the  names  of 
Berzelius  and  Wilhelm   Ostwald.     The  specific  substances 


The  Mechanistic  Conception  of  Life 


which  accelerate  the  oxidations  at  body  temperature  suffi- 
ciently to  allow  the  maintenance  of  life  are  the  so-called 
ferments  of  oxidation. 

The  work  of  Lavoisier  and  Laplace  not  only  marks  the 
beginning  of  scientific  biology,  it  also  touches  the  core  of  the 
problem  of  life;  for  it  seems  that  oxidations  form  a  part,  if 
not  the  basis,  of  all  life  phenomena  in  higher  organisms. 


III.      THE    '^EIDDLE    of    LIFE " 


By  the  ''riddle  of  life"  not  everybody  will  understand  the 
same  thing.  We  all,  however,  desire  to  know  how  life 
originates  and  what  death  is,  since  our  ethics  must  be 
influenced  to  a  large  extent  through  the  answer  to  this  ques- 
tion. We  are  not  yet  able  to  give  an  answer  to  the  question 
as  to  how  life  originated  on  the  earth.  We  know  that  every 
living  being  is  able  to  transform  food-stuffs  into  living  matter; 
and  we  also  know  that  not  only  the  compounds  which  are 
formed  in  the  animal  body  can  be  produced  artificially,  but 
that  chemical  reactions  which  take  place  in  living  organisms 
can  also  be  repeated  at  the  same  rate  and  temperature  in 
the  laboratory.  The  gap  in  our  knowledge  which  we  feel 
most  keenly  is  the  fact  that  the  chemical  character  of  the 
catalyzers  (the  enzymes  or  ferments)  is  still  unknown. 
Nothing  indicates,  however,  at  present  that  the  artificial 
production  of  living  matter  is  beyond  the  possibilities  of 
science.. 

This  view  does  not  stand  in  opposition  to  the  idea  of 
Arrhenius  that  germs  of  sufficiently  small  dimensions  are 
driven  by  radiation-pressure  through  space;  and  that  these 
germs,  if  they  fall  upon  new  cosmic  bodies  possessing  water, 
salts,  and  oxygen,  and  the  proper  temperature,  give  rise  to  a 
new  evolution  of  organisms.  Biology  will  certainly  retain 
this  idea,  but  I  believe  that  we  must  also  follow  out  the 
other  problem :  namely,  we  must  either  succeed  in  producing 


6  The   Mechanistic   Conception  of  Life 

living  matter  artificially,  or  we  must  find  the  reasons  why 
this  is  impossible. 

IV.      THE    activation    OF    THE    EGG 

Although  we  are  not  yet  able  to  state  how  life  originated 
in  general,  another,  more  modest  problem,  has  been  solved, 
that  is,  how  the  egg  is  caused  by  the  sperm  to  develop  into 
a  new  individual.  Every  animal  originates  from  an  egg  and 
in  the  majority  of  animals  a  new  individual  can  only  then 
develop  if  a  male  sex-cell,  a  spermatozoon,  enters  into  the  egg. 
The  question  as  to  how  a  spermatozoon  can  cause  an  egg  to 
develop  into  a  new  individual  was  twelve  years  ago  still 
shrouded  in  that  mystery  which  today  surrounds  the  origin 
of  life  in  general.  But  today  we  are  able  to  state  that  the 
problem  of  the  activation  of  the  egg  is  for  the  most  part 
reduced  to  physico-chemical  terms.  The  egg  is  in  the 
unfertilized  condition  a  single  cell  with  only  one  nucleus. 
If  no  spermatozoon  enters  into  it,  it  perishes  after  a 
comparatively  short  time,  in  some  animals  in  a  few  hours,  in 
others  in  a  few  days  or  weeks.  If,  however,  a  spermatozoon 
enters  into  the  egg,  the  latter  begins  to  develop,  i.e.,  the 
nucleus  begins  to  divide  into  two  nuclei  and  the  egg  which 
heretofore  consisted  of  one  cell  is  divided  into  two  cells. 
Subsequently  each  nucleus  and  each  cell  divides  again  into 
two,  and  so  on.  These  cells  have,  in  many  eggs,  the  tendency 
to  remain  at  the  surface  of  the  egg  or  to  creep  to  the  surface, 
and  later  such  an  egg  forms  a  hollow  sphere  whose  shell  con- 
sists of  a  large  number  of  cells.  On  the  outer  surface  of  this 
hollow  sphere  cilia  are  formed  and  the  egg  is  now  transformed 
into  a  free-swimming  larva.  Then  an  intestine  develops 
through  the  growing  in  of  cells  in  one  region  of  the  blastula 
and  gradually  the  other  organs,  skeleton,  vascular  system, 
etc.,  originate.  Embryologists  had  noticed  that  occasionally 
the  unfertilized  eggs  of  certain  animals,  e.g.,  sea-urchins, 


The  Mechanistic  Conception  of  Life 


worms,  or  even  birds,  show  a  tendency  to  a  nuclear  or  even  a 
cell  division;  and  R.  Hertwig,  Mead,  and  Morgan  had  suc- 
ceeded in  inducing  one  or  more  cell  divisions  artificially  in 
such  eggs.  But  the  cell  divisions  in  these  cases  never  led 
to  the  development  of  a  larva,  but  at  the  best  to  the  formation 
of  an  abnormal  mass  of  cells  which  soon  perished. 

I  succeeded  twelve  years  ago  in  causing  the  unfertilized 
eggs  of  the  sea-urchin  to  develop  into  swimming  larvae  by 
treating  them  with  sea-water,  the  concentration  of  which  was 


Fig.   1 


Fig.  2 


Fig.  1. — Unfertilized  egg  of  the  sea-urchin  surrounded  by  spermatozoa.  Only 
the  heads  of  the  spermatozoa  are  drawn,  since  at  the  magnification  used  the  tails 
were  not  visible. 

Fig.  2. — The  same  egg  immediately  after  the  entrance  of  the  spermatozoon. 
The  egg  is  sm-rounded  by  a  larger  circle,  the  fertilization  membrane,  which  is 
formed  through  the  action  of  the  spermatozoon.  This  formation  of  a  fertilization 
membrane  can  be  induced  by  a  purely  chemical  treatment  of  the  egg. 

raised  through  the  addition  of  a  small  but  definite  quantity 
of  a  salt  or  sugar.  The  eggs  were  put  for  two  hours  into  a 
solution  the  osmotic  pressure  of  which  had  been  raised  to  a 
certain  height.  When  the  eggs  were  put  back  into  normal 
sea-water  they  developed  into  larvae  and  a  part  of  these 
larvae  formed  an  intestine  and  a  skeleton.  The  same  result 
was  obtained  in  the  eggs  of  other  animals,  star-fish,  worms, 
and  mollusks.  These  experiments  proved  the  possibility 
of  substituting  physico-chemical  agencies  for  the  action  of 
the  living  spermatozoon,  but  did  not  yet  explain  how  the 
spermatozoon  causes  the  development  of  the  egg,  since  in 


8  The   Mechanistic  Conception  of  Life 

these  experiments  the  action  of  the  spermatozoon  upon  the 
egg  was  very  incompletely  imitated.  When  a  spermatozoon 
enters  into  the  egg  it  causes  primarily  a  change  in  the  surface 
of  the  egg  which  results  in  the  formation  of  the  so-called 
membrane  of  fertilization.  This  phenomenon  of  membrane 
formation  which  had  always  been  considered  as  a  phenomenon 
of  minor  importance  did  not  occur  in  my  original  method  of 
treating  the  egg  with  hypertonic  sea-water.  Six  years  ago 
while  experimenting  on  the  Californian  sea-urchin,  Strongylo- 
centrotus  purpuratus,  I  succeeded  in  finding  a  method  of 
causing  the  unfertilized  egg  to  form  a  membrane  without 
injuring  the  egg.  This  method  consists  in  treating  the  eggs 
for  from  one  to  two  minutes  with  sea-water  to  which  a  definite 
amount  of  butyric  acid  (or  some  other  monobasic  fatty  acid) 
has  been  added.  If  after  that  time  the  eggs  are  brought  back 
into  normal  sea-water,  all  form  a  fertilization  membrane  in 
exactly  the  same  way  as  if  a  spermatozoon  had  entered. 
This  membrane  formation  or  rather  the  modification  of  the 
surface  of  the  egg  which  underlies  the  membrane  formation 
starts  the  development.  It  does  not  allow  it,  however,  to 
proceed  very  far  at  room  temperature.  In  order  to  allow 
the  development  to  go  farther  it  is  necessary  to  submit  the 
eggs  after  the  butyric  acid  treatment  to  a  second  operation. 
Here  we  have  a  choice  between  two  methods.  We  can 
either  put  the  eggs  for  about  one  half-hour  into  a  hypertonic 
solution  (which  contains  free  oxygen) ;  or  we  can  put  them  for 
about  three  hours  into  sea-water  deprived  of  oxygen.  If  the 
eggs  are  then  returned  to  normal  sea- water  containing  oxygen 
they  all  develop ;  and  in  a  large  number  the  development  is  as 
normal  as  if  a  spermatozoon  had  entered. 

The  essential  feature  is  therefore  the  fact  that  the  develop- 
ment is  caused  by  two  different  treatments  of  the  egg;  and 
that  of  these  the  treatment  resulting  in  the  formation  of 
the  membrane  is  the  more  important  one.     This  is  proved 


The  Mechanistic  Conception  of  Life 


9 


Fig.  3 


Fig.  4 


Fig.  5 

Figs.  3,  4,  and  5. — Segmentation  of  the  sea-urchin  egg,  resulting  in  the 
formation  of  two  ceUs  (Fig.  5).  The  changes  from  Fig.  3  to  Fig.  5  occur  in  about 
one  minute  or  less  time.  This  segmentation  occurs  after  fertilization  or  after  the 
chemical  treatment  of  the  egg  described  in  the  text. 


Fig.  6 


Fig.  7 


Figs.    6   and    7. — The    sea-urchin   egg   divided   into   four   and   eight   cells 
respectively. 


10 


The  Mechanistic  Conception  of  Life 


by  the  fact  that  in  certain  forms,  as  for  instance  the  star-fish, 
the  causation  of  the  artificial  membrane  formation  may 
suffice  for  the  development  of  normal  larvae;  although  here, 
too,  the  second  treatment  increases  not  only  the  number  of 
larvae,  but  also  improves  the  appearance  of  the  larvae,  as 
R.  Lillie  found. 

The  question  now  arises,  how  the  membrane  formation 
can  start  the  development  of  the  egg.     An  analysis  of  the 


Fig.  8 


Fig.  9 


Fig.  8. — Blastnla.  First  larval  stage  of  the  sea-urchin  egg.  At  the  surface 
of  the  cells  cUia  are  formed  and  the  larva  begins  to  swim  and  reaches  the  surface 
of  the  water. 

Fig.  9. — Gastrula  stage.  The  intestine  begins  to  form  and  the  first  indica- 
tion of  the  skeleton  appears  in  the  form  of  fine  crystals. 

process  and  of  the  nature  of  the  agencies  which  cause  it 
yielded  the  result  that  the  unfertilized  egg  possesses  a  super- 
ficial cortical  layer,  which  must  be  destroyed  before  the  egg 
can  develop.  It  is  immaterial  by  what  means  this  superficial 
cortical  layer  is  destroyed.  All  agencies  which  cause  a 
definite  type  of  cell  destruction — the  so-called  cytolysis — 
cause  also  the  egg  to  develop,  as  long  as  their  action  is  limited 
to  the  surface  layer  of  the  cell.  The  butyric  acid  treatment 
of  the  egg  mentioned  above  only  serves  to  induce  the  destruc- 
tion of  this  cortical  layer.  In  the  eggs  of  some  animals  this 
cortical  layer  can  be  destroyed  mechanically  by  shaking  the 


The  Mechanistic  Conception  of  Life 


11 


egg,  as  A.  P.  Mathews  found  in  the  case  of  star-fish  eggs  and  I 
in  the  case  of  the  eggs  of  certain  worms.  In  the  case  of  the 
eggs  of  the  frog  it  suffices  to  pierce  the  cortical  layer  with  a 
needle,  as  Bataillon  found  in  his  beautiful  experiments  a 
year  ago.^  The  mechanism  by 
which  development  is  caused 
is  apparently  the  same  in  all 
these  cases,  namely,  the  de- 
struction of  the  cortical  layer 
of  the  eggs.  This  can  be 
caused  generally  by  certain 
chemical  means  which  play  a 
role  also  in  bacteriology;  but 
it  can  also  be  caused  in  special 
cases  by  mechanical  means, 
such  as  agitation  or  piercing  of 
the  cortical  layer.  It  may  be 
mentioned  parenthetically  that 
foreign  blood  sera  have  also  a 
cytolytic  effect,  and  I  succeeded 
in  causing  membrane  formation  and  in  consequence  the  devel- 
opment of  the  sea-urchin  egg  by  treating  it  with  the  blood  of 
various  animals,  e.g.,  of  cattle,  or  the  rabbit. 

Recently  Shearer  has  succeeded  in  Plymouth  in  causing  a 
number  of  parthenogenetic  plutei  produced  by  my  method  to 
develop  beyond  the  stage  of  metamorphosis,  and  Delage  has 
reported  that  he  raised  two  larvae  of  the  sea-urchin  produced 
by  artificial  parthenogenesis  to  the  stage  of  sexual  maturity. 
We  may,  therefore,  state  that  the  complete  imitation  of  the 
developmental  effect  of  the  spermatozoon  by  certain  physico- 
chemical  agencies  has  been  accomplished. 

I  succeeded  in  showing  that  the  spermatozoon  causes  the 
development  of  the  sea-urchin  egg  in  a  way  similar  to  that 

1  This  method  does  not  work  with  the  eggs  of  fish  and  is  apparently  as  limited 
in  its  applicability  as  the  causation  of  development  by  mechanical  agitation. 


Fig.  10. — Pluteus  stage  of  Strongy- 
locentrotus  purpuratus.  S  skeleton; 
D  intestine. 


12  The  Mechanistic  Conception  of  Life 

in  my  method  of  artificial  parthenogenesis;  namely,  by  carry- 
ing two  substances  into  the  egg,  one  of  which  acts  like  the 
butyric  acid  and  induces  the  membrane  formation,  while 
the  other  acts  like  the  treatment  with  a  hypertonic  solution 
and  enables  the  full  development  of  the  larvae.  In  order  to 
prove  this  for  the  sea-urchin  egg  foreign  sperm,  e.g.,  that  of 
the  star-fish,  must  be  used.  The  sperm  of  the  sea-urchin 
penetrates  so  rapidly  into  the  sea-urchin  egg  that  almost 
always  both  substances  get  into  the  egg.  If,  however,  star- 
fish sperm  is  used  for  the  fertilization  of  the  sea-urchin  egg, 
in  a  large  number  of  cases,  membrane  formation  occurs 
before  the  spermatozoon  has  found  time  to  penetrate  entirely 
into  the  egg.  In  consequence  of  the  membrane  formation 
the  spermatozoon  is  thrown  out.  Such  eggs  behave  as  if 
only  the  membrane  formation  had  been  caused  by  some 
artificial  agency,  e.g.,  butyric  acid.  They  begin  to  develop, 
but  soon  show  signs  of  disintegration.  If  treated  with  a 
hypertonic  solution  they  develop  into  larvae.  In  touching 
the  egg  contents  the  spermatozoon  had  a  chance  to  give  off 
a  substance  which  liquefied  the  cortical  layer  and  thereby 
caused  the  membrane  formation  by  which  the  further 
entrance  of  the  spermatozoon  into  the  egg  was  prevented. 
If,  however,  the  star-fish  sperm  enters  completely  into  the 
egg  before  the  membrane  formation  begins,  the  spermatozoon 
carries  also  the  second  substance  into  the  egg,  the  action  of 
which  corresponds  to  the  treatment  of  the  egg  with  the  hyper- 
tonic solution.  In  this  case  the  egg  can  undergo  complete 
development  into  a  larva. 

F.  Lillie  has  recently  confirmed  the  same  fact  in  the  egg 
of  a  worm,  Nereis.  He  mixed  the  sperm  and  eggs  of  Nereis 
and  centrifuged  the  mass.  In  many  cases  the  spermatozoa 
which  had  begun  to  penetrate  into  the  egg  were  thrown  off 
again.  The  consequence  was  that  only  a  membrane  forma- 
tion resulted  without  the  spermatozoon  penetrating  into  the 


The  Mechanistic  Conception  of  Life  13 

egg.  This  membrane  formation  led  only  to  a  beginning  but 
not  to  a  complete  development.  We  may,  therefore,  con- 
clude that  the  spermatozoon  causes  the  development  of  the 
egg  in  a  way  similar  to  that  which  takes  place  in  the  case  of 
artificial  parthenogenesis.  It  carries  first  a  substance  into 
the  egg  which  destroys  the  cortical  layer  of  the  egg  in  the 
same  way  as  does  butyric  acid;  and  secondly  a  substance 
which  corresponds  in  its  effect  to  the  influence  of  the  hyper- 
tonic solution  in  the  sea-urchin  egg  after  the  membrane 
formation. 

The  question  arises  as  to  how  the  destruction  of  the  corti- 
cal layer  can  cause  the  beginning  of  the  development  of  the 
egg.  This  question  leads  us  to  the  process  of  oxidation. 
Years  ago  I  had  found  that  the  fertilized  sea-urchin  egg  can 
only  develop  in  the  presence  of  free  oxygen;  if  the  oxygen 
is  completely  withdrawn  the  development  stops,  but  begins 
again  promptly  as  soon  as  oxygen  is  again  admitted.  From 
this  and  similar  experiments  I  concluded  that  the  spermato- 
zoon causes  the  development  by  accelerating  the  oxidations 
in  the  egg.  This  conclusion  was  confirmed  by  experiments 
by  O.  Warburg  and  by  Wasteneys  and  myself  in  which  it  was 
found  that  through  the  process  of  fertilization  the  velocity 
of  oxidations  in  the  egg  is  increased  to  four  or  six  times  its 
original  value.  Warburg  was  able  to  show  that  the  mere 
causation  of  the  membrane  formation  by  the  butyric  acid 
treatment  has  the  same  accelerating  effect  upon  the  oxidations 
as  fertilization. 

What  remains  unknown  at  present  is  the  way  in  which 
the  destruction  of  the  cortical  layer  of  the  egg  accelerates  the 
oxidations.  It  is  possible  that  the  cortical  layer  acts  like 
a  solid  crust  and  thus  prevents  the  oxygen  from  reaching 
the  surface  of  the  egg  or  from  penetrating  into  the  latter 
sufficiently  rapidly.  The  solution  of  these  problems  must 
be  reserved  for  further  investigation. 


14  The  Mechanistic  Conception  of  Life 

We  therefore  see  that  the  process  of  the  activation  of 
the  egg  by  the  spermatozoon,  which  twelve  years  ago  was 
shrouded  in  complete  darkness,  is  today  practically  com- 
pletely reduced  to  a  physico-chemical  explanation.  Con- 
sidering the  youth  of  experimental  biology  we  have  a  right 
to  hope  that  what  has  been  accomplished  in  this  problem  will 
occur  in  rapid  succession  in  those  problems  which  today  still 
appear  as  riddles. 

V.      NATURE    OF   LIFE   AND    DEATH 

The  nature  of  life  and  of  death  are  questions  which 
occupy  the  interest  of  the  layman  to  a  greater  extent  than 
possibly  any  other  purely  theoretical  problem;  and  we  can 
well  understand  that  humanity  did  not  wait  for  experimental 
biology  to  furnish  an  answer.  The  answer  assumed  the 
anthropomorphic  form  characteristic  of  all  explanations  of 
nature  in  the  prescientific  period.  Life  was  assumed  to  begin 
with  the  entrance  of  a  ''life  principle"  into  the  body;  that 
individual  life  begins  with  the  egg  was  of  course  unknown  to 
primitive  or  prescientific  man.  Death  was  assumed  to  be 
due  to  the  departure  of  this  ''life  principle"  from  the  body. 

Scientifically,  however,  individual  life  begins  (in  the  case 
of  the  sea-urchin  and  possibly  in  general)  with  the  accelera- 
tion of  the  rate  of  oxidation  in  the  egg,  and  this  acceleration 
begins  after  the  destruction  of  its  cortical  layer.  Life  of 
warm-blooded  animals — man  included — ends  with  the  cessa- 
tion of  oxidation  in  the  body.  As  soon  as  oxidations  have 
ceased  for  some  time,  the  surface  films  of  the  cells,  if  they 
contain  enough  water  and  if  the  temperature  is  sufficiently 
high,  become  permeable  for  bacteria,  and  the  body  is 
destroyed  by  micro-organisms.  The  problem  of  the  begin- 
ning and  end  of  individual  life  is  physico-chemically  clear. 
It  is,  therefore,  unwarranted  to  continue  the  statement  that 
in  addition  to  the  acceleration  of  oxidations  the  beginning  of 


The  Mechanistic  Conception  of  Life  15 

individual  life  is  determined  by  the  entrance  of  a  meta- 
physical ''life  principle"  into  the  egg;  and  that  death  is 
determined,  aside  from  the  cessation  of  oxidations,  by  the 
departure  of  this  ''principle"  from  the  body.  In  the  case  of 
the  evaporation  of  water  we  are  satisfied  with  the  explanation 
given  by  the  kinetic  theory  of  gases  and  do  not  demand  that 
— to  repeat  a  well-known  jest  of  Huxley — the  disappearance 
of  the  "aquosity"  be  also  taken  into  consideration. 

VI.      HEREDITY 

It  may  be  stated  that  the  egg  is  the  essential  bearer  of 
heredity.  We  can  cause  an  egg  to  develop  into  a  larva 
without  sperm,  but  we  cannot  cause  a  spermatozoon  to 
develop  into  a  larva  without  an  egg.  The  spermatozoon 
can  influence  the  form  of  the  offspring  only  when  the  two 
forms  are  rather  closely  related.  If  the  egg  of  a  sea-urchin 
is  fertilized  with  the  sperm  from  a  different  species  of  sea- 
urchin,  the  larval  form  has  distinct  paternal  characters.  If, 
however,  the  eggs  of  a  sea-urchin  are  fertilized  with  the  sperm 
of  a  more  remote  species,  e.g.,  a  star-fish,  the  result  is  a  sea- 
urchin  larva  which  possesses  no  paternal  characters,  as  I 
found  and  as  Godlewski,  Kupelwieser,  Hagedoorn,  and 
Baltzer  were  able  to  confirm.  This  fact  has  some  bearing 
upon  the  further  investigation  of  heredity,  inasmuch  as  it 
shows  that  the  egg  is  the  main  instrument  of  heredity,  while 
apparently  the  spermatozoon  is  restricted  in  the  transmission 
of  characters  to  the  offspring.  If  the  difference  between 
spermatozoon  and  egg  exceeds  a  certain  limit  the  hereditary 
effects  of  the  spermatozoon  cease  and  it  acts  merely  as  an 
activator  to  the  egg. 

As  far  as  the  transmission  of  paternal  characters  is  con- 
cerned, we  can  say  today  that  the  view  of  those  authors  was 
correct  who,  with  Boveri,  localized  this  transmission  not  only 
in  the  cell  nucleus,  but  in  a  special  constituent  of  the  nucleus, 


16  The  Mechanistic  Conception  of  Life 

the  chromosomes.  The  proof  for  this  was  given  by  facts  found 
along  the  lines  of  Mendelian  investigations.  The  essential 
law  of  Mendel,  the  law  of  segregation,  can  in  its  simplest 
form  be  expressed  in  the  following  way.  If  we  cross  two 
forms  which  differ  in  only  one  character  every  hybrid  resulting 
from  this  union  forms  two  kinds  of  sex-cells  in  equal  numbers ; 
two  kinds  of  eggs  if  it  is  a  female,  two  kinds  of  spermatozoa 
if  it  is  a  male.  The  one  kind  corresponds  to  the  pure  paternal, 
the  other  to  the  pure  maternal  type.  The  investigation  of 
the  structure  and  behavior  of  the  nucleus  showed  that  the 
possibility  for  such  a  segregation  of  the  sex-cells  in  a  hybrid 
can  easily  be  recognized  during  a  given  stage  in  the  formation 
of  the  sex-cells,  if  the  assumption  is  made  that  the  chromo- 
somes are  the  bearers  of  the  paternal  characters.  The  proof 
for  the  correctness  of  this  view  was  furnished  through  the 
investigation  of  the  heredity  of  those  qualities  which  occur 
mainly  in  one  sex;  e.g.,  color  blindness  which  occurs  pre- 
eminently in  the  male  members  of  a  family. 

Nine  years  ago  McClung  published  a  paper  which  solved 
the  problem  of  sex  determination,  at  least  in  its  essential 
feature.  Each  animal  has  a  definite  number  of  chromosomes 
in  its  cell  nucleus.  Henking  had  found  that  in  a  certain 
form  of  insects  (Pyrrhocoris)  two  kinds  of  spermatozoa  exist 
which  differ  in  the  fact  that  the  one  possesses  a  nucleolus 
while  the  other  does  not.  Montgomery  afterward  showed 
that  Henking^s  nucleolus  was  an  accessory  chromosome. 
McClung  first  expressed  the  idea  that  this  accessory  chro- 
mosome was  connected  with  the  determination  of  sex.  Con- 
sidering the  importance  of  this  idea  we  may  render  it  in  his 
own  words: 

A  most  significant  fact,  and  one  upon  which  almost  all  investi- 
gators are  united  in  opinion,  is  that  the  element  is  apportioned  to 
but  one-half  of  the  spermatozoa.  Assuming  it  to  be  true  that  the 
chromatin  is  the  important  part  of  the  cell  in  the  matter  of  heredity, 


The  Mechanistic  Conception  of  Life  17 

then  it  follows  that  we  have  two  kinds  of  spermatozoa  that  differ  from 
each  other  in  a  \dtal  matter.  We  expect,  therefore,  to  find  in  the  off- 
spring two  sorts  of  individuals  in  approximately  equal  numbers,  under 
normal  conditions,  that  exhibit  marked  differences  in  structure.  A 
careful  consideration  will  suggest  that  nothing  but  sexual  characters 
thus  di^ddes  the  members  of  a  species  into  two  well-defined  groups, 
and  we  are  logically  forced  to  the  conclusion  that  the  peculiar  chromo- 
some has  some  bearing  upon  the  arrangement. 

I  must  here  also  point  out  a  fact  that  does  not  seem  to  have  the 
recognition  it  deserves;  viz.,  that  if  there  is  a  cross-division  of  the 
chromosomes  in  the  matiuation  mitoses,  there  must  be  two  kinds  of 
spermatozoa  regardless  of  the  presence  of  the  accessory  chromosome. 
It  is  thus  possible  that  even  in  the  absence  of  any  specialized  element 
a  preponderant  maleness  would  attach  to  one-half  of  the  spermatozoa, 
due  to  the  "qualitative  division  of  the  tetrads." 

The  researches  of  the  following  years,  especially  the 
brilliant  work  of  E.  B.  Wilson,  Miss  Stevens,  T.  H.  Morgan, 
and  others,  have  amply  confirmed  the  correctness  of  this 
ingenious  idea  and  cleared  up  the  problem  of  sex  determina- 
tion in  its  main  features. 

According  to  McClung  each  animal  forms  two  kinds  of 
spermatozoa  in  equal  numbers,  which  differ  by  one  chromo- 
some. One  kind  of  spermatozoa  produces  male  animals, 
the  other  female  animals.  The  eggs  are  all  equal  in  these 
animals.  More  recent  investigations,  especially  those  of 
E.  B.  Wilson,  have  shown  that  this  view  is  correct  for  many 
animals. 

While  in  many  animals  there  are  two  kinds  of  sperma- 
tozoa and  only  one  kind  of  eggs,  in  other  animals  two  kinds 
of  eggs  and  only  one  kind  of  spermatozoa  are  formed,  e.g., 
sea-urchins  and  certain  species  of  birds  and  of  butterflies 
(Abraxas).  In  these  animals  the  sex  is  predetermined  in  the 
egg  and  not  in  the  spermatozoon.  It  is  of  interest  that, 
according  to  Guyer,  in  the  human  being  two  kinds  of  sperma- 
tozoa exist  and  only  one  kind  of  eggs;  in  man,  therefore,  sex 
is  determined  by  the  spermatozoon. 


18 


The  Mechanistic  Conception  of  Life 


How  is  sex  determination  accomplished?  Let  us  take 
the  case  which  according  to  Wilson  is  true  for  many  insects 
and  according  to  Guyer  for  human  beings,  namely,  that  there 
are  two  kinds  of  spermatozoa  and  one  kind  of  eggs.  According 
to  Wilson  all  unfertilized  eggs  contain  in  this  case  one  so-called 


Figs.  11-16  (after  E.  B.  Wilson). — Diagrammatic  presentation  of  sex  deter- 
mination in  an  insect  (Protenor).  a  a  are  the  nuclei  of  unfertilized  eggs.  Each 
contains  one  sex  chromosome  marked  X;  the  other  six  dark  spots  are  the  chromo- 
somes which  are  supposed  to  transmit  hereditary  characters  not  connected  with 
sex.  b  and  c  represent  the  two  different  types  of  sperm;  6  containing  a  sex 
chromosome  X,  c  being  without  such  a  chromosome. 

d  represents  the  constitution  of  the  egg  nucleus  after  it  is  fertilized  by  a 
spermatozoon  of  the  type  b  containing  a  sex  chromosome.  This  egg  now  has  two 
sex  chromosomes  and  therefore  will  give  rise  to  a  female,  e  represents  a  fertilized 
egg  after  a  spermatozoon  of  the  type  c  (without  a  sex  chromosome)  has  entered  it. 
This  egg  contains  after  fertilization  only  one  sex  chromosome  X  and  hence  will 
give  rise  to  a  male. 

sex  chromosome,  the  X-chromosome.  There  are  two  kinds 
of  spermatozoa,  one  with  and  one  without  an  X-chromosome. 
Given  a  sufficiently  large  number  of  eggs  and  of  spermatozoa, 
one-half  of  the  eggs  will  be  fertilized  by  spermatozoa  with 
and  one-half  by  spermatozoa  without  an  X-chromosome. 
Hence  one-half  of  the  eggs  will  contain  after  fertilization  two 
X-chromosomes  each  and  one-half  only  one  X-chromosome 


The  Mechanistic  Conception  of  Life  19 

each.  The  eggs  containing  only  one  X-chromosome  give 
rise  to  males,  those  containing  two  X-chromosomes  give  rise 
to  females — as  Wilson  and  others  have  proved.  This  seems 
to  be  a  general  law  for  those  cases  in  which  there  are  two 
kinds  of  spermatozoa  and  one  kind  of  eggs. 

These  observations  show  why  it  is  impossible  to  influence 
the  sex  of  a  developing  embryo  by  external  influences.  If, 
for  example,  in  the  human  being  a  spermatozoon  without  an 
X-chromosome  enters  into  an  egg,  the  egg  will  give  rise  to  a 
boy,  but  if  a  spermatozoon  with  an  X-chromosome  gets  into 
the  egg  the  latter  will  give  rise  to  a  girl.  Since  always  both 
kinds  of  spermatozoa  are  given  off  by  the  male  it  is  a  mere 
matter  of  chance  whether  a  boy  or  a  girl  originates;  and 
it  agrees  with  the  law  of  probability  that  in  a  large  popula- 
tion the  number  of  boys  and  girls  born  within  a  year  is 
approximately  the  same.^ 

These  discoveries  solved  also  a  series  of  other  difficulties. 
Certain  types  of  twins  originate  from  one  egg  after  fertiliza- 
tion. Such  twins  have  always  the  same  sex,  as  we  should 
expect,  since  the  cells  of  both  twins  have  the  same  number  of 
X-chromosomes. 

In  plant  lice,  bees,  and  ants,  the  eggs  may  develop  with 
and  without  fertilization.  It  was  known  that  from  fertilized 
eggs  in  these  animals  only  females  develop,  males  never. 
It  was  found  that  in  these  animals  the  eggs  contain  only  one 
sex  chromosome;  while  in  the  male  are  found  two  kinds  of 
spermatozoa,  one  with  and  one  without  a  sex  chromosome. 
For  Phylloxera  and  Aphides  it  has  been  proved  with  certainty 
by  Morgan  and  others  that  the  spermatozoa  which  contain  no 
sex  chromosome  cannot  live,  and  the  same  is  probably  true 
for  bees  and  ants.     If,  therefore,  in  these  animals  an  egg  is 

1  It  is  stated  that  the  number  of  males  born  exceeds  that  of  the  females  by  a 
slight  percentage.  If  this  statement  is  correct  it  must  be  due  to  a  secondary- 
cause,  e.g.,  a  greater  motility  or  greater  duration  of  life  of  the  male  spermatozoon. 
Further  researches  will  be  needed  to  clear  up  this  point. 


20  The  Mechanistic  Conception  of  Life 

fertilized  it  is  always  done  by  a  spermatozoon  which  contains 
an  X-chromosome.  The  egg  has,  therefore,  after  fertilization 
in  these  animals  always  two  X-chromosomes  and  from  such 
eggs  only  females  can  arise. 

It  had  been  known  for  a  long  time  that  in  bees  and  ants 
the  unfertilized  eggs  can  also  develop,  but  such  eggs  give 
rise  to  males  only.  This  is  due  to  the  fact  that  the  eggs  of 
these  animals  contain  only  one  X-chromosome  and  from  eggs 
with  only  one  chromosome  only  males  can  arise  (at  least  in  the 
case  of  animals  in  which  the  male  is  heterozygous  for  sex). 

The  problem  of  sex  determination  has,  therefore,  found  a 
simple  solution,  and  simultaneously  Mendel's  law  of  segrega- 
tion also  finds  its  solution. 

In  many  insects  and  in  man  the  cells  of  the  female  have 
two  sex  chromosomes.  In  a  certain  stage  of  the  history  of  the 
egg  one-half  of  the  chromosomes  leave  the  egg  (in  the  form 
of  the  ''polar-body")  and  it  keeps  only  half  the  number  of 
chromosomes.  Each  egg,  therefore,  retains  only  one  X  or 
sex  chroraosome.  In  the  male  the  cells  have  from  the  begin- 
ning only  one  X-chromosome  and  each  primordial  sperma- 
tozoon divides  into  two  new  (in  reality  into  two  pairs  of) 
spermatozoa,  one  of  which  contains  an  X-chromosome 
while  the  other  is  without  such  a  chromosome.  What  can  be 
observed  here  directly  in  the  male  animal  takes  place  in 
every  hybrid;  during  the  critical,  so-called  maturation  divi- 
sion of  the  sexual  cell  in  the  hybrid,  a  division  of  the  chromo- 
somes occurs,  whereby  only  one-half  of  the  sex-cells  receive 
the  hereditary  substance  in  regard  to  which  the  two  original 
pure  forms  differ. 

That  this  is  not  a  mere  assumption  can  be  shown  in  those 
cases  in  which  the  hereditary  character  appears  only,  or  pre- 
eminently, in  one  sex  as,  e.g.,  color  blindness  which  appears 
mostly  in  the  male.  If  a  color-blind  individual  is  mated  with 
an  individual  with  normal  color  vision  the  heredity  of  color 


The  Mechanistic  Conception  of  Life  21 

blindness  in  the  next  two  generations  corresponds  quantita- 
tively with  what  we  must  expect  on  the  assumption  that  the 
chemical  substances  determining  color  vision  are  contained 
in  the  sex  chromosomes.  In  the  color-blind  individual  some- 
thing is  lacking  which  can  be  found  in  the  individual  with 
normal  color  perception.  The  factor  for  color  vision  is  obvi- 
ously transmitted  through  the  sex  chromosome.  In  the  next 
generation  color  blindness  cannot  appear,  since  each  fertilized 
egg  contains  the  factor  for  color  perception.  In  the  second 
generation,  however,  the  theory  demands  that  one-half  of  the 
males  should  be  color  blind.  In  man  these  conditions  cannot 
be  verified.  T.  H.  Morgan  has  found  in  a  fly  (Drosophila)  a 
number  of  similar  sex-limited  characters  which  behave  like 
color  blindness,  e.g.,  lack  of  pigment  in  the  eyes.  These 
flies  have  normally  red  eyes.  Morgan  has  observed  a  muta- 
tion with  white  eyes,  which  occurs  in  the  male.  When  he 
crossed  a  white-eyed  with  a  red-eyed  female  all  flies  of  the 
first  generation  were  red-eyed,  since  all  flies  had  the  factor 
for  pigment  in  their  sex-cells;  in  the  second  generation  all 
females  and  exactly  one-half  of  the  males  had  red  eyes,  the 
other  half  of  the  males,  however,  white  eyes,  as  the  theory 
demands. 

From  these  and  numerous  similar  breeding  experiments  of 
Correns,  Doncaster,  and  especially  of  Morgan,  we  may  con- 
clude Avith  certainty  that  the  sex  chromosomes  are  the  bearers 
of  those  hereditary  characters  which  appear  pre-eminently  in 
one  sex.  We  say  pre-eminently,  since  theoretically  we  can 
predict  cases  in  which  color  blindness  or  white  eyes  must  appear 
also  in  the  female.  Breeding  experiments  have  shown  that  this 
theoretical  prediction  is  justified.  The  riddle  of  Mendel's  law 
of  segregation  finds  its  solution  through  these  experiments  and 
incidentally  also  the  problem  of  the  determination  of  sex  which 
is  only  a  special  case  of  the  law  of  segregation,  as  Mendel 
already  intimated. 


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Vj3 


The  Mechanistic  Conception  of  Life  23 

The  main  task  which  is  left  here  for  science  to  accomplish  is 
the  determination  of  the  chemical  substances  in  the  chromo- 
somes which  are  responsible  for  the  hereditary  transmission  of 
a  quality,  and  the  determination  of  the  mechanism  by  which 
these  substances  give  rise  to  the  hereditary  character.  Here 
the  ground  has  already  been  broken.  It  is  known  that  for  the 
formation  of  a  certain  black  pigment  the  cooperation  of  a 
substance — tyrosin — and  of  a  ferment  of  oxidation — tyrosinase 
— ^is  required.  The  hereditary  transmission  of  the  black  color 
through  the  male  animal  must  occur  by  substances  carried  in 
the  chromosome  which  determine  the  formation  of  tyrosin  or 
tyrosinase  or  of  both.  We  may,  therefore,  say  that  the  solu- 
tion of  the  riddle  of  heredity  has  succeeded  to  the  extent  that 
all  further  development  will  take  place  purely  in  cytological 
and  physico-chemical  terms. 

While  until  twelve  years  ago  the  field  of  heredity  was  the 
stamping  ground  for  the  rhetorician  and  metaphysician  it  is 
today  perhaps  the  most  exact  and  rationalistic  part  of  biology, 
where  facts  cannot  only  be  predicted  qualitatively,  but  also 
quantitatively. 

VII.  THE  HARMONIOUS  CHARACTER  OF  THE  ORGANISMS 

It  is  not  possible  to  prove  in  a  short  address  that  all  life 
phenomena  will  yield  to  a  physico-chemical  analysis.  We  have 
selected  only  the  phenomena  of  fertilization  and  heredity,  since 
these  phenomena  are  specific  for  living  organisms  and  without 
analogues  in  inanimate  nature;  and  if  we  can  convince  our- 
selves that  these  processes  can  be  explained  physico-chemically 
we  may  safely  expect  the  same  of  such  processes  for  which 
there  exist  a-priori  analogies  in  inanimate  nature,  as,  e.g.,  for 
absorption  and  secretion. 

We  must,  however,  settle  a  question  which  offers  itself 
not  only  to  the  layman  but  also  to  every  biologist,  namely,  how 
we  shall  conceive  that  wonderful  "  adaptation  of  each  part  to  the 


24  The  Mechanistic  Conception  of  Life 

whole  "  by  which  an  organism  becomes  possible.  In  the  answer 
to  this  question  the  metaphysician  finds  an  opportunity  to  put 
above  the  purely  chemical  and  physical  processes  something 
specific  which  is  characteristic  of  life  only:  the  ''Zielstrebigkeit/' 
the  ''harmony"  of  the  phenomena,  or  the  ''dominants"  of 
Reinke  and  similar  things. 

With  all  due  personal  respect  for  the  authors  of  such  terms 
I  am  of  the  opinion  that  we  are  dealing  here,  as  in  all  cases  of 
metaphysics,  with  a  play  on  words.  That  a  part  is  so  con- 
structed that  it  serves  the  "whole"  is  only  an  unclear  expression 
for  the  fact  that  a  species  is  only  able  to  live — or  to  use  Roux's 
expression — is  only  durable,  if  it  is  provided  with  the  automatic 
mechanism  for  self-preservation  and  reproduction.  If,  for 
instance,  warm-blooded  animals  should  originate  without  a 
circulation  they  could  not  remain  alive,  and  this  is  the  reason 
why  we  never  find  such  forms.  The  phenomena  of  "adapta- 
tion" cause  only  apparent  difficulties  since  we  rarely  or  never 
become  aware  of  the  numerous  faultily  constructed  organisms 
which  appear  in  nature.  I  will  illustrate  by  a  concrete  example 
that  the  number  of  species  which  we  observe  is  only  an  infinitely 
small  fraction  of  those  which  can  originate  and  possibly  not 
rarely  do  originate,  but  which  we  never  see  since  their  organiza- 
tion does  not  allow  them  to  continue  to  exist  long.  Moenk- 
haus  found  ten  years  ago  that  it  is  possible  to  fertilize  the  egg 
of  each  marine  bony  fish  with  the  sperm  of  practically  any 
other  marine  bony  fish.  His  embryos  apparently  lived  only 
a  very  short  time.  This  year  I  succeeded  in  keeping  such 
hybrid  embryos  between  distantly  related  bony  fish  alive  for 
over  a  month.  It  is,  therefore,  clear  that  it  is  possible  to  cross 
practically  any  marine  teleost  with  any  other. 

The  number  of  teleosts  at  present  in  existence  is  about 
10,000.  If  we  accomplish  all  possible  hybridizations  100,000,000 
different  crosses  will  result.  Of  these  teleosts  only  a  very  small 
proportion,  namely  about  one  one-hundredth  of  1  per  cent, 


The  Mechanistic  Conception  of  Life  25 

can  live.  It  turned  out  in  my  experiments  that  the  heterogene- 
ous hybrids  between  bony  fishes  formed  eyes,  brains,  ears,  fins, 
and  pulsating  hearts,  blood  and  blood-vessels,  but  could  live 
only  a  limited  time  because  no  blood  circulation  was  established 
— ^in  spite  of  the  fact  that  the  heart  beat  for  weeks — or  that  the 
circulation,  if  it  was  established  at  all,  did  not  last  long. 

What  prevented  these  heterogeneous  fish  embryos  from 
reaching  the  adult  stage?  The  lack  of  the  proper  ''domi- 
nants''?  Scarcely.  I  succeeded  in  producing  the  same  type 
of  faulty  embryos  in  the  pure  breeds  of  a  bony  fish  (Fundulus 
heterocUtus)  by  raising  the  eggs  in  50  c.c.  of  sea-water  to  which 
was  added  2  c.c.  1/100  per  cent  NaCN.  The  latter  substance 
retards  the  velocity  of  oxidations  and  I  obtained  embryos 
which  were  in  all  details  identical  with  the  embryos  produced 
by  crossing  the  eggs  of  the  same  fish  with  the  sperm  of  remote 
teleosts,  e.g.,  Ctenolabrus  or  Menidia.  These  embryos,  which 
lived  about  a  month,  showed  the  peculiarity  of  possessing  a 
beating  heart  and  blood,  but  no  circulation.  This  suggests  \ 
the  idea  that  heterogeneous  embryos  show  a  lack  of  "adapta- 
tion" and  durability  for  the  reason  that  in  consequence  of  the 
chemical  difference  between  heterogeneous  sperm  and  egg  the 
chemical  processes  in  the  fertilized  egg  are  abnormal. 

The  possibility  of  hybridization  goes  much  farther  than  we 
have  thus  far  assumed.  We  can  cause  the  eggs  of  echinoderms 
to  develop  with  the  sperm  of  very  distant  forms,  even  mollusks 
and  worms  (Kupelwieser) ;  but  such  hybridizations  never  lead 
to  the  formation  of  durable  organisms. 

It  is,  therefore,  no  exaggeration  to  state  that  the  number  of 
species  existing  today  is  only  an  infinitely  small  fraction  of 
those  which  can  and  possibly  occasionally  do  originate,  but 
which  escape  our  notice  because  they  cannot  live  and  reproduce. 
Only  that  limited  fraction  of  species  can  exist  which  possesses 
no  coarse  disharmonies  in  its  automatic  mechanism  of  preserva- 
tion and  reproduction.     Disharmonies  and  faulty  attempts  in 


26  The  Mechanistic  Conception  of  Life 

nature  are  the  rule,  the  harmonically  developed  systems  the  rare 
exception.  But  smce  we  only  perceive  the  latter  we  gain  the 
erroneous  impression  that  the  ''adaptation  of  the  parts  to  the 
plan  of  the  whole"  is  a  general  and  specific  characteristic  of  ani- 
mate nature,  whereby  the  latter  differs  from  inanimate  nature. 
If  the  structure  and  the  mechanism  of  the  atoms  were 
known  to  us  we  should  probably  also  get  an  insight  into  a  world 
of  wonderful  harmonies  and  apparent  adaptations  of  the  parts 
to  the  whole.  But  in  this  case  we  should  quickly  understand 
that  the  chemical  elements  are  only  the  few  durable  systems 
among  a  large  number  of  possible  but  not  durable  combinations. 
Nobody  doubts  that  the  durable  chemical  elements  are  only 
the  product  of  blind  forces.  There  is  no  reason  for  conceiving 
otherwise  the  durable  systems  in  living  nature. 

VIII.    THE   CONTENTS   OF  LIFE 

The  contents  of  life  from  the  cradle  to  the  bier  are  wishes 
and  hopes,  efforts  and  struggles,  and  unfortunately  also  dis- 
appointments and  suffering.  And  this  inner  life  should  be 
amenable  to  a  physico-chemical  analysis?  In  spite  of  the 
gulf  which  separates  us  today  from  such  an  aim  I  believe  that 
it  is  attainable.  As  long  as  a  life  phenomenon  has  not  yet  found 
a  physico-chemical  explanation  it  usually  appears  inexplicable. 
If  the  veil  is  once  lifted  we  are  always  surprised  that  we  did 
not  guess  from  the  first  what  was  behind  it. 

That  in  the  case  of  our  inner  life  a  physico-chemical  explana- 
tion is  not  beyond  the  realm  of  possibility  is  proved  by  the  fact 
that  it  is  already  possible  for  us  to  explain  cases  of  simple  mani- 
festations of  animal  instinct  and  will  on  a  physico-chemical 
basis;  namely,  the  phenomena  which  I  have  discussed  in  former 
papers  under  the  name  of  animal  tropisms.  As  the  most 
simple  example  we  may  mention  the  tendency  of  certain  ani- 
mals to  fiy  or  creep  to  the  light.  We  are  dealing  in  this  case 
with  the  manifestation  of  an  instinct  or  impulse  which  the 


The  Mechanistic  Conception  of  Life  27 

animals  cannot  resist.  It  appears  as  if  this  blind  instinct  which 
these  animals  must  follow,  although  it  may  cost  them  their  life, 
might  be  explained  by  the  same  law  of  Bunsen  and  Roscoe, 
which  explains  the  photochemical  effects  in  inanimate  nature. 
This  law  states  that  within  wide  limits  the  photochemical  effect 
equals  the  product  of  the  intensity  of  light  into  the  duration 
of  illumination.  It  is  not  possible  to  enter  here  into  all  the 
details  of  the  reactions  of  these  animals  to  light ;  we  only  wish 
to  point  out  in  which  way  the  light  instinct  of  the  animals 
may  possibly  be  connected  with  the  Bunsen-Roscoe  law. 

The  positively  heliotropic  animals — i.e.,  the  animals  which 
go  instinctively  to  a  source  of  light — have  in  their  eyes  (and 
occasionally  also  in  their  skin)  photosensitive  substances  which 
undergo  chemical  alterations  by  light.  The  products  formed 
in  this  process  influence  the  contraction  of  the  muscles — mostly 
indirectly,  through  the  central  nervous  system.  If  the  animal 
is  illuminated  on  one  side  only,  the  mass  of  photochemical 
reaction  products  formed  on  that  side  in  the  unit  of  time  is 
greater  than  on  the  opposite  side.  Consequently  the  develop- 
ment of  energy  in  the  symmetrical  muscles  on  both  sides  of  the 
body  becomes  unequal.  As  soon  as  the  difference  in  the  masses 
of  the  photochemical  reaction  products  on  both  sides  of  the 
animal  reaches  a  certain  value,  the  animal,  as  soon  as  it  moves, 
is  automatically  forced  to  turn  toward  one  side.  As  soon  as 
it  has  turned  so  far  that  its  plane  of  symmetry  is  in  the  direction 
of  the  rays,  the  symmetrical  spots  of  its  surface  are  struck  by 
the  light  at  the  same  angle  and  in  this  case  the  intensity  of  light 
and  consequently  the  velocity  of  reaction  of  the  photochemical 
processes  on  both  sides  of  the  animal  become  equal.  There 
is  no  more  reason  for  the  animal  to  deviate  from  the  motion  in 
a  straight  line  and  the  positively  heliotropic  animal  will  move 
in  this  line  to  the  source  of  light.  (It  was  assumed  that  in 
these  experiments  the  animal  is  under  the  influence  of  only 
one  source  of  light  and  positively  heliotropic.) 


28 


The  Mechanistic  Conception  of  Life 


In  a  series  of  experiments  I  have  shown  that  the  heliotropic 
reactions  of  animals  are  identical  with  the  heliotropic  reactions 
of  plants.     It  was  known  that  sessile  heliotropic  plants  bend 


Fig.  18 


Fig.  19 

Figs.  18  and  19. — Positive  heliotropism  of  the  polyps  of  Eudendrium.  The 
new  polyp-bearing  stems  all  grow  in  the  direction  of  the  rays  of  light  which  is 
indicated  by  an  arrow  in  each  figure.  (From  nature.)  These  animals  bend  in 
the  same  way  to  the  light  as  the  stems  of  positively  heliotropic  plants  kept  imder 
similar  conditions. 

their  stems  to  the  source  of  light  until  the  axis  of  symmetry  of 
their  tip  is  in  the  direction  of  the  rays  of  light.  I  found  the 
same  phenomenon  in  sessile  animals,  e.g.,  certain  hydroids 
and  worms.  Motile  plant  organs,  e.g.,  the  swarm  spores  of 
plants,  move  to  the  source  of  light  (or  if  they  are  negatively 


The  Mechanistic  Conception  of  Life 


29 


heliotropic  away  from  it),  and  the  same  is  observed  in  motile 
animals.  In  plants  only  the  more  refrangible  rays  from  green  to 
blue  have  these  heliotropic  effects,  while  the  red  and  yellow 
rays  are  little  or  less  effective;  and  the  same  is  true  for  the 
heliotropic  reactions  of  animals. 

It  has  been  shown  by  Blaauw  for  the  heliotropic  curvatures 
of  plants  that  the  product  of  the  intensity  of  a  source  of  light 
into  the  time  required  to  induce  a  heliotropic  curvature  is  a 


Fig.  20. — Positive  heliotropism  of  a  marine  worm  (Spirographis).  (From 
nature.)  The  light  fell  into  the  aquariimi  from  one  side  only  and  the  worms  all 
bent  their  heads  toward  the  source  of  light,  as  the  stems  of  positively  heliotropic 
plants  would  do  under  the  same  conditions. 

constant;  and  the  same  result  was  obtained  simultaneously 
by  another  botanist,  Froschl.  It  is  thus  proved  that  the  Bunsen- 
Roscoe  law  controls  the  heliotropic  reactions  of  plants.  The 
same  fact  had  already  been  proved  for  the  action  of  light  on  our 
retina. 

The  direct  measurements  in  regard  to  the  applicability  of 
Bunsen's  law  to  the  phenomena  of  animal  heUotropism  have  not 
yet  been  made.  But  a  number  of  data  point  to  the  probability 
that  the  law  holds  good  here  also.  The  first  of  these  facts  is 
the  identity  of  the  light  reactions  of  plants  and  animals.  The 
second  is  at  least  a  rough  observation  which  harmonizes  with 
the  Bunsen-Roscoe  law.  As  long  as  the  intensity  of  light  or 
the  mass  of  photochemical  substances  at  the  surfaces  of  the 


30  The  Mechanistic  Conception  of  Life 

animal  is  small,  according  to  the  law  of  Bunsen,  it  must  take  a 
comparatively  long  time  until  the  animal  is  automatically 
oriented  by  the  light,  since  according  to  this  law  the  photo- 
chemical effect  is  equal  to  the  product  of  the  intensity  of  the 
light  into  the  duration  of  illumination.  If,  however,  the  inten- 
sity of  the  light  is  strong  or  the  active  mass  of  the  photochemical 
substance  great,  it  will  require  only  a  very  short  time  until  the 
difference  in  the  mass  of  photochemical  reaction  products  on 
both  sides  of  the  animal  reaches  the  value  which  is  necessary 
for  the  automatic  turning  to  (or  from)  the  light.  The  behavior 
of  the  animals  agrees  with  this  assumption.  If  the  light  is 
sufficiently  strong  the  animals  go  in  an  almost  straight  line  to 
the  source  of  light;  if  the  intensity  of  light  (or  the  mass  of 
photosensitive  substances  on  the  surface  of  the  animal)  is 
small  the  animals  go  in  irregular  lines,  but  at  last  they  also 
land  at  the  source  of  light,  since  the  directing  force  is  not 
entirely  abolished.  It  will,  however,  be  necessary  to  ascertain 
by  direct  measurements  to  what  extent  these  phenomena  in 
animals  are  the  expression  of  Bunsen-Roscoe's  law.  But  we  may 
already  safely  state  that  the  apparent  will  or  instinct  of  these 
animals  resolves  itself  into  a  modification  of  the  action  of 
the  muscles  through  the  influence  of  light;  and  for  the  meta- 
physical term  ''will"  we  may  in  these  instances  safely  substi- 
tute the  chemical  term  ''photochemical  action  of  light." 

Our  wishes  and  hopes,  disappointments  and  sufferings  have 
their  source  in  instincts  which  are  comparable  to  the  light 
instinct  of  the  heliotropic  animals.  The  need  of  and  the 
struggle  for  food,  the  sexual  instinct  with  its  poetry  and  its 
chain  of  consequences,  the  maternal  instincts  with  the  felicity 
and  the  suffering  caused  by  them,  the  instinct  of  workmanship, 
and  some  other  instincts  are  the  roots  from  which  our  inner  life 
develops.  For  some  of  these  instincts  the  chemical  basis  is  at 
least  sufficiently  indicated  to  arouse  the  hope  that  their  analysis, 
from  the  mechanistic  point  of  view,  is  only  a  question  of  time. 


The  Mechanistic  Conception  of  Life  31 

ix.   ethics 

If  our  existence  is  based  on  the  play  of  blind  forces  and  only 
a  matter  of  chance ;  if  we  ourselves  are  only  chemical  mechan- 
isms— how  can  there  be  an  ethics  for  us?  The  answer  is, 
that  our  instincts  are  the  root  of  our  ethics  and  that  the  instincts 
are  just  as  hereditary  as  is  the  form  of  our  body.  We  eat, 
drink,  and  reproduce  not  because  mankind  has  reached  an 
agreement  that  this  is  desirable,  but  because,  machine-like, 
we  are  compelled  to  do  so.  We  are  active,  because  we  are  com- 
pelled to  be  so  by  processes  in  our  central  nervous  system; 
and  as  long  as  human  beings  are  not  economic  slaves  the  instinct 
of  successful  work  or  of  workmanship  determines  the  direction 
of  their  action.  The  mother  loves  and  cares  for  her  children, 
not  because  metaphysicians  had  the  idea  that  this  was  desirable, 
but  because  the  instinct  of  taking  care  of  the  young  is  inherited 
just  as  distinctly  as  the  morphological  characters  of  the  female 
body.  We  seek  and  enjoy  the  fellowship  of  human  beings 
because  hereditary  conditions  compel  us  to  do  so.  We  struggle 
for  justice  and  truth  since  we  are  instinctively  compelled  to  see 
our  fellow  beings  happy.  Economic,  social,  and  political  con- 
ditions or  ignorance  and  superstition  may  warp  and  inhibit 
the  inherited  instincts  and  thus  create  a  civilization  with  a 
faulty  or  low  development  of  ethics.  Individual  mutants  may 
arise  in  which  one  or  the  other  desirable  instinct  is  lost,  just  as 
individual  mutants  without  pigment  may  arise  in  animals;  and 
the  offspring  of  such  mutants  may,  if  numerous  enough,  lower 
the  ethical  status  of  a  community.  Not  only  is  the  mechanistic 
conception  of  life  compatible  with  ethics :  it  seems  the  only  con- 
ception of  life  which  can  lead  to  an  imderstanding  of  the  source 
of  ethics. 


II.    THE  SIGNIFICANCE  OF  TROPISMS  FOR 
PSYCHOLOGY 


II 

THE  SIGNIFICANCE    OF   TROPISMS  FOR  PSYCHOLOGYi 

I 

A  mechanistic  conception  of  life  is  not  complete  unless  it 
includes  a  physico-chemical  explanation  of  psychic  phenomena. 
Some  authors  hold  that  even  if  a  complete  physico-chemical 
analysis  of  these  phenomena  were  possible  today  it  would  leave 
the  ''truly  psychical"  imexplained.  We  do  not  need  to  enter 
into  a  discussion  of  such  an  objection  since  we  are  still  too  far 
from  the  goal.  We  are  at  least  able  to  show  for  a  limited  group 
of  animal  reactions  that  they  can  be  explained  unequivocally  on 
a  purely  physico-chemical  basis,  namely,  phenomena  which  the 
metaphysician  would  classify  under  the  term  of  animal  ''will." 

Through  the  writings  of  Schopenhauer  and  E.  von  Hart- 
mann  I  became  interested  in  the  problem  of  will.  When  as  a 
student  I  read  Munk's  investigations  on  the  cerebral  cortex 
I  believed  that  they  might  serve  as  a  starting-point  for  an 
experimental  analysis  of  will.  Munk  stated  that  he  had 
succeeded  in  proving  that  every  memory  image  in  a  dog's 
brain  is  localized  in  a  particular  cell  or  group  of  cells  and  that 
any  one  of  these  memory  images  can  be  extirpated  at  desire. 
Five  years  of  experiments  with  extirpations  in  the  cerebral 
cortex  proved  to  me  without  doubt  that  Munk  had  become  the 
victim  of  an  error  and  that  the  method  of  cerebral  operations 
may  give  data  concerning  the  path  of  nerves  in  the  central 
nervous  system  but  that  it  teaches  little  about  the  djmamics  of 
brain  processes. 

A  better  opportunity  seemed  to  offer  itself  in  the  study 
of  the  comparative  psychology  of  the  lower  animals  in  which 

1  Lectixre  delivered  at  the  Sixth  International  Psychological  Congress  at 
Geneva,  1909.  (After  a  translation  in  Popular  Science  Monthly  by  Miss  Grace  B. 
Watkinson.)     Reprinted  by  courtesy  of  Professor  James  McKeen  Cattell. 

35 


36  The  Mechanistic  Conception  of  Life 

the  mechanism  for  memory  is  developed  but  sHghtly  or  not  at 
all.  It  seemed  to  me  that  some  day  it  must  become  possible 
to  discover  the  physico-chemical  laws  underlying  the  apparently 
random  movements  of  such  animals;  and  that  the  word  "  animal 
will"  was  only  the  expression  of  our  ignorance  of  the  forces 
which  prescribe  to  animals  the  direction  of  their  apparently 
spontaneous  movements  just  as  unequivocally  as  gravity 
prescribes  the  movements  of  the  planets.  For  if  a  savage 
could  directly  observe  the  movements  of  the  planets  and  should 
begin  to  think  about  them,  he  would  probably  come  to  the  con- 
clusion that  a  ''will  action"  guides  the  movements  of  the  planets 
just  as  a  chance  observer  is  today  inclined  to  assume  that  ''will" 
causes  animals  to  move  in  a  given  direction. 

The  scientific  solution  of  the  problem  of  will  seemed  then 
to  consist  in  finding  the  forces  which  determine  the  movements 
of  animals,  and  in  discovering  the  laws  according  to  which 
these  forces  act.  Experimentally,  the  solution  of  the  problem 
of  will  must  take  the  form  of  forcing,  by  external  agencies,  any 
number  of  individuals  of  a  given  kind  of  animals  to  move  in 
a  definite  direction  by  means  of  their  locomotor  apparatus. 
Only  if  we  succeed  in  this  have  we  the  right  to  assume  that  we 
know  the  force  which  under  certain  conditions  seems  to  a  lay- 
man to  be  the  will  of  the  animal.  But  if  one  part  only  of  the 
animals  moves  in  this  definite  direction  and  the  other  does  not, 
we  have  not  succeeded  in  finding  the  force  which  unequivocally 
determines  the  direction  of  their  movement. 

One  other  point  should  be  observed.  If  a  sparrow  flies 
down  to  a  seed  lying  on  the  ground,  we  speak  of  an  act  of  will, 
but  if  a  dead  sparrow  falls  upon  the  seed  this  does  not  appear 
to  us  as  such.  In  the  latter  case  purely  physical  forces  are 
concerned,  while  in  the  former  chemical  reactions  are  also  tak- 
ing place  in  the  sense-organs,  nerves,  and  muscles  of  the  animal. 
We  speak  of  an  act  of  will,  only  when  this  latter  complex,  that 
is,  the  natural  movement  of  locomotion,  plays  its  part  also,  and 


Significance  of  Tropisms  for  Psychology      37 

it  is  only  with  this  sort  of  reactions  that  we  have  to  deal  in  the 
psychology  of  the  will. 

II 

Some  experiments  on  winged  plant  lice  may  serve  as  an 
introduction  to  the  methods  of  prescribing  to  animals  the 
direction  of  their  progressive  movements. 

In  order  to  obtain  the  material,  potted  rose  bushes  or  Cine- 
rarias infected  with  plant  lice  are  brought  into  a  room  and 
placed  in  front  of  a  closed  window.  If  the  plants  are  allowed 
to  dry  out,  the  aphids  (plant  lice),  previously  wingless,  change 
into  winged  insects.  After  this  metamorphosis  the  animals 
leave  the  plants,  fly  to  the  window,  and  there  creep  upward 
on  the  glass.  They  can  then  easily  be  collected  by  holding  a 
test-tube  underneath  and  touching  one  animal  at  a  time  from 
above  with  a  pen  or  scalpel,  which  causes  the  animals  to  drop 
into  the  test-tube.  In  this  manner  a  sufficiently  large  number, 
perhaps  twenty-five  or  fifty  suitable  subjects  for  the  experi- 
ment, may  be  obtained.  With  these  animals  it  may  be  demon- 
strated that  the  direction  of  their  movement  toward  the  light 
is  definitely  determined — provided  that  the  animals  are  healthy 
and  that  the  light  is  not  too  weak.  The  experiment  is  so  arranged 
that  only  a  single  source  of  light,  e.g.,  artificial  light,  is  used. 

The  animals  place  themselves  with  their  heads  toward  the 
source  of  light  and  move  toward  it  in  as  straight  a  line  as  the 
imperfection  of  their  locomotor  apparatus  allows,  approaching  as 
near  to  the  source  of  light  as  their  prison  (the  test-tube)  permits. 
When  they  reach  that  end  of  the  test-tube  which  is  directed 
toward  the  source  of  light,  they  remain  there,  stationary,  in  a 
closely  crowded  mass.  If  the  test-tube  is  turned  180°  the 
animals  again  go  straight  toward  the  source  of  light  imtil  the 
interference  of  the  glass  stops  their  further  progressive  move- 
ments.^    It  can  be  demonstrated  in  these  animals  that  the 

1  Loeb,  Der  Heliotropismus  der  Tiere  und  seine  Uebereinstimmung  mit  dem 
Heliotropismus  der  Pflanzen,  Wiirzburg,  1889.  Translated  in  Studies  in  General 
Physiology,  1906. 


38  The  Mechanistic  Conception  of  Life 

direction  of  their  progressive  movement  is  just  as  unequivocally 
governed  by  the  source  of  light  as  the  direction  of  the  move- 
ment of  the  planets  is  determined  by  the  force  of  gravity. 

The  theory  of  the  compulsory  movements  of  aphids  under 
the  influence  of  light  is  as  follows :  Two  factors  govern  the  pro- 
gressive movements  of  the  animals  under  these  conditions; 
one  is  the  symmetrical  structure  of  the  animal,  and  the  second 
is  the  photochemical  action  of  light.  We  will  consider  the 
two  separately.  In  regard  to  the  photochemical  action  of  light, 
we  know  today  that  a  great  many  chemical  reactions  of  organic 
bodies  are  accelerated  by  light.  Especially  is  this  true  of  oxi- 
dations.^  The  mass  of  facts  is  already  so  great  that  we  are 
justified  in  assuming  that  the  determining  action  of  light  upon 
animals  and  plants  is  in  its  last  analysis  due  to  the  fact  that  the 
rate  of  certain  chemical  reactions  in  the  cells  of  the  retina  or 
of  other  photosensitive  regions  of  the  organisms  is  modified 
by  light;  with  increasing  intensity  of  light  the  rate  of  certain 
chemical  reactions,  e.g.,  oxidation,  increases. 

The  second  factor  is  the  symmetrical  structure  of  the  ani- 
mal. As  expressed  in  the  gross  anatomy  of  the  animal,  the 
right  and  left  halves  of  the  body  are  symmetrical.  But  it  is 
my  belief  that  such  a  symmetry  exists  in  a  chemical  sense,  as 
well  as  in  an  anatomical,  by  which  I  mean  that  symmetrical 
regions  of  the  body  are  chemically  identical  and  have  the  same 
metabolism,  while  non-symmetrical  regions  of  the  body  are 
chemically  different,  and  in  general  have  a  quantitatively  or 
qualitatively  different  metabolism.  In  order  to  illustrate  this 
difference  it  is  only  necessary  to  point  out  that  the  two  retinae, 
which  are  certainly  symmetrical,  have  an  identical  metabolism, 
while  a  region  of  the  skin  which  is  not  symmetrical  with  the 
retina  has  a  different  metabolism.     The  individual  points  on 

1  Luther,  Die  Aufgaben  der  Photochemie,  Leipzig,  1905;  C.  Neuberg,  Biochem. 
Zeitschr.,  Xlll,  305,  1908;  Loeb,  The  Dynamics  of  Living  Matter,  New  York,  1906. 
In  addition,  see  ttie  work  of  Ciamician,  as  also  of  Wolfgang  Ostwald  (Biochem. 
Zeitschr.,  1907). 


Significance  of  Tropisms  for  Psychology      39 

the  retina  are  also  chemically  unlike.  The  observations  upon 
visual  purple,  the  differences  in  the  color  sensitiveness  of  the 
fovea  centralis,  and  the  peripheral  parts  of  the  retina  indicate 
that  the  points  of  symmetry  of  the  two  retinae  are  chemically 
alike,  the  non-symmetrical  points  chemically  unlike. 

Now  if  an  imequal  amount  of  light  falls  upon  the  two 
retinae  the  photochemical  reactions  in  the  one  which  receives 
more  light  will  also  be  more  accelerated  than  those  in  the  other. 
The  same  naturally  holds  true  for  every  other  pair  of  sym- 
metrical photosensitive  surface  elements.  For  it  should  be 
mentioned  that  photochemical  substances  are  not  found  in 
the  eyes  only,  but  also  in  other  places  on  the  surface  of  many 
animals.  In  planarians,  as  my  experiments  and  those  of 
Parker  have  shown,  not  only  the  eyes,  but  also  parts  of  the 
skin,  are  photosensitive.  But  if  more  light  falls  upon  one 
retina  than  upon  the  other,  the  chemical  reactions  will  also  be 
more  accelerated  in  the  one  retina  than  in  the  other,  and 
accordingly  more  intense  chemical  changes  will  take  place  in 
one  optic  nerve  than  in  the  other.  S.  S.  Maxwell  and  C.  D. 
Snyder  have  demonstrated,  independently  of  each  other,  that 
the  rate  of  the  nerve  impulse  has  a  temperature  coeflS.cient  of 
the  order  of  magnitude  which  is  characteristic  for  chemical 
reactions.  From  this  we  must  conclude  that  when  two  retinae 
(or  other  points  of  symmetry)  are  illuminated  with  unequal 
intensity,  chemical  processes,  also  of  unequal  intensity,  take 
place  in  the  two  optic  nerves  (or  in  the  sensory  nerves  of  the 
two  illuminated  points) .  This  inequality  of  chemical  processes 
passes  from  the  sensory  to  the  motor  nerves  and  eventually  to 
the  muscles  connected  with  them.  We  conclude  from  this 
that  with  equal  illumination  of  both  retinae  the  symmetrical 
groups  of  muscles  of  both  halves  of  the  body  will  receive  equal 
chemical  stimuli  and  thus  reach  equal  states  of  contraction, 
while,  when  the  rate  of  reaction  is  unequal,  the  symmetrical 
muscles  on  one  side  of  the  body  come  into  stronger  action  than 


40  The  Mechanistic  Conception  op  Life 

those  on  the  other  side.  The  result  of  such  an  inequality  of  the 
action  of  symmetrical  muscles  of  the  two  sides  of  the  body  is 
a  change  in  the  direction  of  movement  on  the  part  of  the  animal. 

The  change  in  the  direction  of  movement  can  result  either 
in  a  turning  of  the  head  and,  in  consequence,  of  the  whole  animal 
toward  the  source  of  light,  or  in  a  turning  of  the  head  and  the 
animal  in  the  opposite  direction.  The  structure  of  the  central 
nervous  system  is  segmental  and  the  head  segments  generally 
determine^  the  behavior  of  the  other  segments  with  their  acces- 
sory parts. 

In  the  winged  aphids  the  relations  are  as  follows :  Suppose 
that  a  single  source  of  light  is  present  and  that  the  light  strikes 
the  animal  from  one  side.  As  a  consequence  the  activity  of 
those  muscles  which  turn  the  head  or  body  of  the  animal  toward 
the  source  of  light  will  be  increased. ^  As  a  result  the  head,  and 
with  it  the  whole  body  of  the  animal,  is  turned  toward  the 
source  of  light.  As  soon  as  this  happens,  the  two  retinae 
become  illuminated  equally.  There  is  therefore  no  longer 
any  cause  for  the  animal  to  turn  in  one  direction  or  the  other. 
It  is  thus  automatically  guided  toward  the  source  of  light. 
In  this  instance  the  light  is  the  ''will"  of  the  animal  which 
determines  the  direction  of  its  movement,  just  as  it  is  gravity 
in  the  case  of  a  falling  stone  or  the  movement  of  a  planet.  The 
action  of  gravity  upon  the  movement  of  the  falling  stone  is 
direct,  while  the  action  of  light  upon  the  direction  of  movement 
of  the  aphids  is  indirect,  inasmuch  as  the  animal  is  caused 
only  by  means  of  an  acceleration  of  photochemical  reactions 
to  move  in  a  definite  direction. 

1  Loeb,  Comparative  Physiology  of  the  Brain  and  Comparative  Psychology,  New 
York  and  London,  1900. 

'  If  two  sources  of  light  of  equal  intensity  are  at  an  equal  distance  from  the 
animal,  it  will  move  in  a  direction  at  right  angles  to  a  line  connecting  the  two 
sources  of  light,  because  in  this  base  both  eyes  are  similarly  influenced  by  the  light. 
Herein,  as  Bohn  has  rightly  said,  the  machine-like  heliotropic  reaction  of  animals 
differs  from  the  movement  of  a  human  being  toward  one  of  two  sources  of  light, 
the  movement  in  the  latter  case  not  being  determined  by  heUotropism. 


Significance  of  Tropisms  for  Psychology      41 

We  will  now  designate  as  positively  heliotropic  those  animals 
which  are  forced  to  turn  their  head  or  move  toward  the  source 
of  light,  and  as  negatively  heliotropic  those  animals  which  are 
oriented  or  compelled  to  move  in  the  opposite  direction.^ 

The  aphids  serve  here  only  as  an  example.  The  same  phe- 
nomena of  positive  heliotropism  may  be  demonstrated  with 
equal  precision  in  a  great  many  animals,  vertebrates  as  well  as 
invertebrates.  We  cannot,  of  course,  give  here  an  account  of 
all  these  cases.  The  reader  who  is  interested  in  them  must  look 
into  the  voluminous  literature  upon  this  subject.  Heliotropism 
is  unusually  common  among  the  larvae  of  marine  animals  and 
insects,  but  also  not  lacking  in  sexually  mature  individuals. 

Heliotropic  animals  are  therefore  in  reality  photometric 
machines.  According  to  photometric  laws  the  intensity  of 
light  varies  with  the  sine  of  the  angle  at  which  the  light  strikes 
a  surface  element  of  the  animal  (or  with  the  cosine  of  the  angle 
of  incidence).  The  animal  is  oriented  by  the  light  in  such  a 
way  that  symmetrical  elements  of  its  photosensitive  surface 
are  struck  at  about  the  same  angle.  In  the  presence  of  only 
one  source  of  light  this  condition  is  fulfilled  if  the  axis  of  sym- 
metry of  the  animal  moves  in  the  direction  of  the  rays  of  light. 
In  this  case  the  velocity  of  photochemical  reactions  on  both  sides 
of  the  animal  is  the  same  and  there  is  no  reason  why  it  should 
deviate  from  this  direction  in  its  progressive  motions. 

Experiments  on  the  heliotropism  of  plants  as  well  as  on  the 
perception  of  light  by  our  retina  have  shown  that  the  effect  of 
light  equals  the  product  of  the  intensity  into  the  duration 
of  illumination.  This  law  is  identical  with  the  general  law  of 
Bunsen  and  Roscoe  which  states  that  the  chemical  effect 
of  light  is  within  wide  limits  equal  to  this  product.  We  do 
not  yet  know  whether  or  not  Bunsen's  law  holds  good  for  the 
heliotropic  animals.     If  it  does,  we  shall  have  to  substitute 

1  Whether  an  animal  is  positively  or  negatively  heliotropic  depends  upon  the 
fact  whether  the  light  causes  an  increase  or  a  decrease  in  the  tension  of  the  muscles . 
Why  light  should  have  these  opposite  effects  is  as  yet  unknown. 


42  The  Mechanistic  Conception  of  Life 

this  law  for  what  the  metaphysician  calls  the  will  of  these 
animals. 

Ill 

The  winged  aphids  serve  as  an  example,  because  they  fulfil 
the  above-mentioned  requirement,  namely,  that  all  individuals, 
without  exception,  move  toward  the  light.  For  mechanistic 
science  it  is  a  methodological  postulate  that  the  same  law  acts 
without  exception,  or  that  the  exception  must  be  satisfactorily 
explained.  It  was  soon  found,  as  was  to  be  expected,  that  not 
all  organisms  in  their  natural  condition  are  equally  suitable 
for  these  experiments.  Many  animals  show  no  heliotropism 
at  all ;  many  show  only  a  slight  reaction,  while  others  show  it  in 
a  degree  as  pronounced  as  do  the  winged  aphids.  The  problem 
therefore  presented  itself  of  producing  heliotropism  artificially 
in  animals  which,  imder  natural  conditions,  show  no  positive 
heliotropism.  If  small  crustaceans  of  a  fresh-water  pond  or 
lake  are  taken  with  a  plankton  net  at  noontime  or  in  the  after- 
noon and  placed  in  an  aquarium  which  is  illuminated  from  one 
side  only,  it  is  often  found  that  these  animals  move  about  in 
the  vessel  pretty  much  at  random  and  distribute  themselves 
irregularly.  Some  seem  to  go  more  toward  the  source  of  light, 
others  in  the  opposite  direction,  and  the  majority  perhaps  pay 
no  attention  to  the  light. 

This  condition  changes  instantly  if  we  add  to  the  water 
some  acid,  preferably  carbonic  acid,  which  easily  penetrates  the 
cells  of  the  animal.  To  every  50  c.c.  of  the  fresh  water  a  few 
cubic  centimeters  of  water  charged  with  carbon  dioxide  are 
slowly  added.  If  the  correct  amount  is  added  all  the  individuals 
become  actively  positively  heliotropic  and  move  in  as  straight 
a  line  as  the  imperfection  of  their  swimming  movements  per- 
mits, toward  the  source  of  light,  and  remain  there  closely 
crowded  together  on  the  illuminated  side  of  the  vessel.  If  the 
vessel  is  turned  180°,  they  go  directly  back  again  to  the  lighted 
side  of  the  vessel.     Every  other  acid  acts  like  carbonic  acid  and 


Significance  of  Tropisms  for  Psychology      43 

alcohol  acts  in  the  same  manner,  only  more  weakly  and  much 
more  slowly.  Animals  which  were  previously  indifferent  to 
light  become,  imder  carbonic  acid  treatment,  complete  slaves 
of  the  light.i 

How  does  the  acid  produce  this  result?  We  will  assume 
that  it  acts  as  a  sensitizer.  The  light  produces  chemical 
changes,  for  instance,  oxidation,  on  the  surface  of  the  animal, 
especially  in  the  eye,  as  was  suggested  in  the  case  of  the  aphids. 
The  mass  of  photochemical  substance  which  is  acted  upon  by 
the  light  is  often  relatively  small,  so  that  even  when  the  light 
strikes  the  crustacean  (copepod)  on  one  side  only,  the  difference 
in  the  chemical  changes  on  the  two  sides  of  the  body  remains 
still  too  small  to  call  forth  a  difference  in  tension  or  action  in  the 
muscles  of  the  two  sides  of  the  body,  sufficient  to  turn  the  ani- 
mal toward  the  source  of  light.  But  if  we  add  an  acid  this  could 
act  as  a  catalyzer,  as,  for  instance,  in  the  catalysis  of  esters. 
In  the  catalysis  of  esters,  the  acid  acts,  according  to  Stieglitz, 
only  to  the  extent  of  increasing  the  active  mass  of  the  substance 
which  undergoes  a  chemical  change.  In  order  to  fix  our  ideas 
provisionally  we  will  assume  that  the  acid  makes  the  animal 
more  strongly  positively  heliotropic  by  increasing  the  active 
mass  of  the  photosensitive  substance.  In  this  way  the  same 
intensity  of  light  which  before  produced  no  heliotropic  reaction 
now  may  cause  a  very  pronounced  positively  heliotropic  reac- 
tion; because  if  now  the  animal  is  struck  on  one  side  only  by 
the  light,  the  difference  in  the  reaction  products  in  both  retinae 
becomes  rapidly  large  enough  to  cause  automatically  a  differ- 
ence in  the  action  of  the  muscles  of  both  sides  of  the  body  and  a 
turning  of  the  head  toward  the  source  of  light. 

In  certain  forms,  for  instance,  in  Daphnia  and  in  certain 
marine  copepods,  a  decrease  in  temperature  also  increases  the 
tendency  to  positive  heliotropism.  If  the  mere  addition  of 
acid  is  not  sufficient  to  make  Daphniae  positively  heliotropic, 

1  Loeb,  P fingers  Archiv,  CXV,  564,  1906. 


44  The  Mechanistic  Conception  of  Life 

this  may  often  be  accomplished  by  simultaneously  reducing  the 
temperature. 

IV 
The  animals  which  are  strongly  positively  heliotropic  and 
those  animals  which  do  not  react  at  all  to  light  offer  no  diffi- 
culties to  the  observer.  Nevertheless,  some  zoologists  seem  to 
have  found  difficulty  in  explaining  the  behavior  of  those  animals 
which  come  between  the  two  extremes.  For  instance,  one  writer 
has  asserted  that  with  greater  intensity  of  light  the  laws  of 
heliotropic  orientation  hold  good,  while  with  a  lessened  light 
intensity  the  animals  react  to  light  by  the  method  of  ''trial 
and  error.''  From  a  chemical  standpoint  the  behavior  of 
animals  at  low  intensity  is  easily  to  be  understood.  If  a  posi- 
tively heliotropic  animal  is  illuminated  from  one  side,  a  com- 
pulsory turning  of  the  head  toward  the  source  of  light  occurs 
only  when  the  difference  in  the  rate  of  certain  photochemical 
reactions  in  the  two  eyes  reaches  a  certain  value.  If  the  inten- 
sity of  the  light  is  sufficient  and  the  active  mass  of  photochemical 
substance  in  the  animal  great  enough,  it  requires  only  a  short 
time,  for  instance,  the  fraction  of  a  second,  before  the  difference 
in  the  mass  of  the  reaction  products  formed  on  the  two  sides 
of  the  animal  reaches  the  value  necessary  for  the  compulsory 
turning  of  the  head  toward  the  source  of  light.  In  this  case  the 
animal  is  a  slave  of  the  light;  in  other  words,  it  has  hardly  time 
to  deviate  from  the  direction  of  the  light  rays;  for  if  it  turns 
the  head  even  for  the  fraction  of  a  second  from  the  direction 
of  the  light  rays,  the  difference  in  the  photochemical  reaction 
products  in  the  two  retinae  becomes  so  great  that  the  head  is 
at  once  turned  back  automatically  toward  the  source  of  light. 
But  if  the  intensity  of  the  light  or  the  photosensitiveness  of 
the  animal  is  lessened  the  animal  may  deviate  for  a  longer 
period  from  the  direction  of  the  light  rays.  Such  animals 
do  eventually  reach  the  lighted  side  of  the  vessel,  but  they  no 
longer  go  straight  toward  it,  moving  instead  in  zig-zag  lines 


Significance  of  Tropisms  for  Psychology      45 

or  very  irregularly.  It  is  therefore  not  a  case  of  a  qualitative, 
but  of  a  quantitative,  difference  in  the  behavior  of  heliotropic 
animals  under  greater  or  lesser  illumination,  and  it  is  there- 
fore erroneous  to  assert  that  heliotropism  determines  the 
movement  of  animals  toward  the  source  of  light  only  under 
strong  illumination,  but  that  under  weaker  illumination  an 
essentially  different  condition  exists. 

Still  another  point  is  to  be  considered.  We  have  seen 
that  acid  increases  the  sensitiveness  of  certain  animals  to  light, 
possibly  by  increasing  the  active  mass  of  the  photochemical 
substance.  Every  animal  is  continually  producing  acids  in  its 
cells,  especially  carbonic  acid  and  lactic  acid;  and  such  acids 
increase  the  tendency  in  certain  animals  to  react  heliotropically. 
It  probably  produces  also  substances  which  could  have  the 
opposite  effect  and  which  decrease  the  heliotropic  sensitiveness 
of  the  animals.  Fluctuations  in  the  rate  of  the  production  of 
these  substances  will  also  produce  fluctuations  in  the  helio- 
tropic sensitiveness  of  the  animal.  If,  for  instance,  the  active 
mass  of  the  photosensitive  substance  in  a  copepod  is  relatively 
small,  a  temporary  increase  in  the  production  of  carbonic  acid 
can  increase  the  photosensitiveness  of  the  animal  sufficiently 
to  cause  it  to  move  for  the  period  of  a  few  seconds  directly 
toward  the  source  of  light.  Later  the  production  of  carbonic 
acid  decreases  and  the  animal  again  becomes  indifferent  to  light 
and  can  move  in  any  direction.  Then  the  production  of  car- 
bonic acid  increases  again  and  the  animal  goes  again,  for  a 
short  time,  toward  the  light.  Such  animals  finally  gather  at 
the  lighted  side  of  the  vessel  because  the  algebraic  sum  of  the 
movements  in  the  other  directions  becomes  zero  according  to 
the  law  of  chance.  But  it  is  plain  that  such  animals  do  not 
reach  the  source  of  light  by  a  straight  path.  A  writer  who  is 
not  trained  to  interpret  the  variations  in  the  behavior  of  such 
an  animal  chemically  and  physiologically,  can  naturally  give 
no  explanation  of  their  significance.     If  he  is  forced  to  find  an 


46  The  Mechanistic  Conception  of  Life 

explanation  he  will  wind  up  with  the  suggestion  of  ''trial  and 
error"  which  is  no  more  chemical  or  scientific  than  the  explana- 
tions of  metaphysicians  in  general. 

Some  authors  have,  it  seems,  worked  only  with  animals 
which  were  not  pronouncedly  heliotropic  and  whose  photo- 
sensitiveness  wavered  about  the  threshold  of  stimulation  in  the 
manner  described  above.  Such  animals  are  not  suitable  for 
experiments  in  heliotropism  and  it  is  necessary  to  first  increase 
their  photosensitiveness  if  the  laws  of  the  action  of  light  upon 
them  are  to  be  investigated. 

I  also  believe  that  observations  upon  animals  which  are 
not  sufficiently  photosensitive  have  caused  many  writers  to 
assert  that  heliotropic  animals  do  not  place  themselves  directly 
in  the  line  of  the  rays  of  light,^  but  that  they  first  have  to  learn 
the  right  orientation.  A  very  striking  experiment  contradicts 
this  assertion.  The  larvae  of  Balanus  perforatus  develop 
entirely  in  the  dark.  If  the  ovary  filled  with  mature  larvae 
is  placed  in  a  watch  crystal  filled  with  sea-water  in  the  dark, 
the  larvae  emerge  at  once  and,  if  they  are  brought  into  the  light, 
they  move  at  once  to  the  side  of  the  watch  crystal  nearest  to 
the  window.  They  were,  therefore,  pronouncedly  positively 
heliotropic  before  they  came  under  the  influence  of  the  light. 

In  experiments  with  winged  aphids  I  often  found  that 
after  having  gone  through  the  heliotropic  reactions  a  few  times 
they  react  much  more  quickly  to  light  than  at  the  beginning. 
This  might  be  interpreted  as  a  case  of  ''learning."  In  so  far 
as  it  is  not  a  case  of  a  lessening  of  the  stickiness  of  the  feet  or 
the  removal  of  some  other  purely  mechanical  factor  which 
retards  the  rate  of  movement,  it  may  be  brought  about  by  the 
carbonic  or  lactic  acids  produced  through  the  muscular  activity .^ 

1  Provided  that  only  a  single  source  of  light  is  present. 

2  The  so-caUed  "  staircase  "  phenomenon  of  stimulation  of  a  muscle  is  ascribed, 
probably  rightly,  also  to  the  formation  of  acid.  This  phenomenon,  that  is,  the 
increase  of  the  amount  of  contraction  with  every  new  stimulus,  is,  however,  com- 
parable to  or  identical  with  the  increase  in  the  rate  of  reactions  in  the  experiments 
described  here. 


Significance  of  Tkopisms  for  Psychology      47 

V 

As  far  back  as  1889  I  pointed  out  that  the  photosensitive- 
ness  of  an  animal  is  different  in  different  physiological  conditions 
and  that,  therefore,  under  natural  conditions,  heliotropism  is 
found  often  only  in  certain  developmental  stages,  or  in  certain 
physiological  states  of  an  animal.  I  have  already  mentioned 
that  in  the  aphids  distinct  heliotropic  reactions  may  only  be 
expected  when  the  animals  have  developed  wings  and  have  left 
the  plant.  The  influence  of  the  chemical  changes  which  take 
place  in  animals  upon  heliotropism  is  much  more  distinct  in 
the  larvae  of  Porthesia  chrysorrhoea.  The  larvae  hatch  from 
the  eggs  in  the  fall  and,  as  young  larvae,  hibernate  in  a  nest. 
The  rising  temperature  in  the  spring  drives  them  out  of  the 
nest,  and  they  can  also  be  driven  out  of  the  nest  in  winter  by 
an  increase  in  temperature.  When  driven  out  of  the  nest  in 
this  condition  they  are  strongly  positively  heliotropic  and  I 
have  never  found  in  natural  surroundings  any  animals  whose 
heliotropic  sensitiveness  was  more  pronounced  than  it  is  in  the 
young  larvae  of  Chrysorrhoea.  But  as  soon  as  the  animals 
have  once  eaten,  the  positive  heliotropism  disappears  and  does 
not  return  even  if  they  are  again  allowed  to  become  hungry.^ 
In  this  case  it  is  clear  that  the  chemical  changes  directly  or 
indirectly  connected  with  nutrition  lead  to  a  permanent  dimi- 
nution or  disappearance  of  the  photochemical  reaction.  In 
ants  and  bees  the  influence  of  substances  from  the  sexual 
organs  seems  to  be  the  determining  factor  in  the  production  of 
positive  heliotropism.  The  ant  workers  show  no  heliotropic 
reactions,  while  in  the  males  and  females,  at  the  time  of  sexual 
maturity,  a  distinct  positive  heliotropism  develops,  the  intensity 
of  which  continues  to  increase. 

It  is  a  well-known  fact  that  during  sexual  maturity  special 
substances  are  formed  which   influence  various  organs.     For 

1  Loeb,  op.  cit.,  p.  24.  (This  latter  fact  has  been  overlooked  by  several 
writers.) 


48  The  Mechanistic  Conception  of  Life 

instance,  Leo  Loeb  has  found  that  the  substances  which  are 
set  free  by  the  bursting  of  an  egg  follicle  cause  a  special  sensi- 
tiveness in  the  non-pregnant  uterus,  so  that  every  mechanical 
stimulus  causes  the  latter  to  form  a  decidua.  In  this  way  he 
could  cause  the  formation  of  any  number  of  deciduae  in  non- 
pregnant uteri,  while  without  the  circulation  of  follicle  sub- 
stance in  the  blood  the  uterus  did  not  react  in  this  manner. 

It  is  a  common  phenomenon  that  animals  in  certain  larval 
stages  are  positively  heliotropic,  while  in  others  they  are  not 
sensitive  to  light  or  are  even  negatively  heliotropic.  I  will 
not  discuss  these  facts  further  in  this  place,  but  refer  my  readers 
to  my  earlier  papers. 

This  change  in  the  heliotropic  sensitiveness,  produced  by 
certain  metabolic  products  in  the  animal  body,  is  of  great  biologi- 
cal significance.  I  pointed  out  in  former  papers  that  it  serves 
to  save  the  lives  of  the  above-mentioned  young  larvae  of  Chrysor- 
rhoea.  When  the  young  larvae  are  awakened  from  their  winter 
sleep  by  the  sunshine  of  the  spring  they  are  positively  helio- 
tropic. Their  positive  heliotropism  leaves  them  no  freedom 
of  movement,  but  forces  them  to  creep  straight  upward  to  the 
top  of  a  tree  or  branch.  Here  they  find  the  first  buds.  In  this 
way  their  heliotropism  guides  them  to  their  food.  Should 
they  now  remain  positively  heliotropic  they  would  be  held  fast 
on  the  ends  of  the  twigs  and  would  starve  to  death.  But  we 
have  already  mentioned  that  after  having  eaten  they  once  more 
lose  their  positive  heliotropism.  They  can  now  creep  down- 
ward, and  the  restlessness  which  is  characteristic  of  so  many 
animals^  forces  them  to  creep  downward  until  they  reach  a 
new  leaf,  the  odor  or  tactile  stimulus  of  which  stops  the  pro- 
gressive movement  of  the  machine  and  sets  their  eating 
activity  again  in  motion. 

The  fact  that  ants  and  bees  become  positively  heliotropic 
at  the  time  of  sexual  maturity  plays  an  important  role  in  the 

1  The  physico-chemical  cause  of  this  "restlessness"  which  is  noticeable  in 
many  insects  and  crustaceans  is  at  present  unknown. 


Significance  of  Tropisms  for  Psychology      49 

vital  economy  of  these  creatures.  As  is  well  known,  the  mating 
of  these  insects  takes  place  during  the  so-called  nuptial  flight. 
I  found  that  among  the  male  and  female  ants  of  a  nest  the 
heliotropic  sensitiveness  increases  steadily  up  to  the  time  of 
the  nuptial  flight  and  that  the  direction  of  their  flight  follows 
the  direction  of  the  rays  of  the  sun.  I  gained  the  impression 
that  this  nuptial  flight  is  merely  the  consequence  of  a  very 
highly  developed  heliotropic  sensitiveness.  The  case  seems  to 
be  similar  among  the  bees  according  to  the  following  experi- 
ment described  by  Kellogg.  The  bees  were  ready  to  swarm 
out  of  the  opening  of  the  box  used  for  the  experiment  when 
he  suddenly  removed  the  dark  covering  of  the  box  so  that  the 
light  now  entered  it  from  above.  The  heliotropic  sensitiveness 
of  the  animals  was  so  great  that  they  crept  upward  within 
the  box,  following  the  direction  of  the  light  rays,  and  were  not 
able  to  make  the  nuptial  flight.  Thus,  according  to  these  obser- 
vations the  bees  at  the  time  of  the  nuptial  flight  are  positively 
heliotropic  machines. 

These  observations  may  serve  as  examples  of  the  way  in 
which  the  analysis  of  the  vital  phenomena  of  certain  animals 
shows  tropisms  to  be  elements  of  these  phenomena.  Many 
observations  of  a  similar  nature  are  found  in  the  papers  of 
Georges  Bohn,  Parker,  Radl,^  and  myself. 

VI 

Under  the  influence  of  the  theory  of  natural  selection  the 
view  has  been  accepted  by  many  zoologists  and  psychologists 
that  everything  which  an  animal  does  is  for  its  best  interest. 
The  exact  doctrine  of  heredity,  founded  by  Mendel  and 
advanced  to  the  position  of  a  systematic  science  in  1900, 
reduces  this  idea  to  its  proper  value.  It  is  only  true  that 
species  possessing  tropisms  which  would  make  reproduction 
and  preservation  of  the  species  impossible  must  die  out. 

1  Radl,  Der  Phototropismus  der  Tiere,  Leipzig,  1903. 


50  The  Mechanistic  Conception  of  Life 

Galvanotropism  illustrates  this  fact  in  a  striking  manner. 
If  a  galvanic  current  is  passed  through  a  trough  filled  with 
water,  and  animals  are  placed  in  this  trough,  it  can  be  observed 
that  an  orientation  in  relation  to  the  direction  of  the  current 
takes  place  in  many  of  the  animals,  and  that  they  move  in  the 
direction  either  of  the  positive  or  of  the  negative  current. 
This  phenomenon  we  call  galvanotropism.  In  galvanotropism 
the  current  lines  or  the  current  curves  play  the  same  role  as  the 
light  rays  in  heliotropism.  At  those  points  where  the  current 
curves  enter  the  cells^  a  collection  of  ions  takes  place  which 
influences  the  chemical  reactions.  The  number  of  species 
which  show  typical  galvanotropic  reactions  is  not  so  great  as  the 
number  of  those  showing  typical  heliotropism.  In  my  opinion 
this  difference  is  the  result  of  the  physical  difference  in  the  action 
of  light  and  of  the  electric  current.  Light  acts  essentially 
upon  the  free  surface  of  the  animal,  while  the  electric  current 
affects  all  the  cells  and  nerves.  Thus  the  action  of  the  current 
upon  the  skin  becomes  complicated  and  modified  by  its  simul- 
taneous effect  upon  the  nerve  branches  and  upon  the  central 
nervous  system.  The  result  is  thus  much  more  complicated 
than  that  of  the  action  of  light  where  essentially  only  the  effect 
upon  the  skin  and  retina  is  involved.  For  this  reason,  a  dis- 
tinct galvanotropism  is  found  more  often  in  organisms  with 
a  simple  structure,  as,  for  instance,  in  unicellular  organisms, 
than  in  vertebrates,  although  it  is  also  demonstrable  in  the 
latter. 

Galvanotropism  is,  however,  purely  a  laboratory  product. 
With  the  exception  of  a  few  individuals,  which  have  in  recent 
years  fallen  into  the  hands  of  physiologists  who  happened  to  be 
working  on  galvanotropism,  no  animal  has  ever  had  the  chance 
to  come  under  the  influence  of  an  electric  current.  And  yet 
galvanotropism  is  a  remarkably  common  reaction  among 
animals.     A  more  direct  contradiction  of  the  view  that  the 

1  Or  where  the  movement  of  the  ions  within  the  ceU  is  retarded. 


Significance  of  Tropisms  for  Psychology      51 

reactions  of  animals  are  determined  by  their  needs  or  by  natural 
selection  could  hardly  be  found. 

One  might  be  led  to  suppose  that  galvanotropism  and  heli- 
otropism  are  not  comparable.  They  are,  however,  as  a  matter 
of  fact,  phenomena  of  the  same  category  with  the  exception  of 
the  aforementioned  fact,  that  light  acts  generally  only  upon  the 
surface  of  the  skin,  while  the  electric  current  influences  all  the 
cells  of  the  body.  As  already  mentioned,  the  disturbing  com- 
plications arising  from  this  latter  circumstance  disappear  for 
the  most  part  when  we  work  with  unicellular  organisms,  and  we 
should  expect  that  galvanic  and  heliotropic  reactions  would 
more  nearly  resemble  one  another  in  this  case,  provided  that 
we  work  with  organisms  possessing  both  forms  of  sensitiveness. 
And  this  expectation  is  fulfilled.  The  algae  of  the  species 
Volvox  show  heliotropism  and  galvanotropism.  The  investi- 
gations made  by  Holmes  and  myself  upon  heliotropism,  as  well 
as  those  of  Bancroft  upon  the  galvanotropism  of  these  organisms 
indicate  that  the  mechanism  of  these  reactions  in  Volvox  is 
the  same  and  the  degree  of  determinism  of  the  heliotropic 
and  galvanotropic  reactions  in  Volvox  is  equally  great. 

Claparede  raises  the  objection  that  the  galvanotropic 
reactions  are  purely  compulsory,  while  the  heliotropic  reactions 
are  governed  by  the  ''interest  of  the  animal."^  Such  a  view, 
however,  is  not  supported  by  the  facts.  The  reason  why  heli- 
otropism may  occasionally,  as  we  have  seen,  be  of  use,  while 
galvanotropism  has  no  biological  significance,  is  because  the 
electric  current  does  not  exist  in  nature.  It  can,  however,  be 
shown  also  that  heliotropism  is  just  as  useless  to  many  animals 
as  galvanotropism.  For  instance,  I  pointed  out  twenty  years 
ago  that  some  varieties  of  animals  which  do  not  live  in  the  light 
at  all,  for  instance,  the  larvae  of  the  goat  moth,  which  live  under 
the  bark  of  trees,  may  show  positive  heliotropism.  I  found, 
moreover,  that  the  crab,  Cuma  Rathkii,  which  lives  in  the  mud  of 

1  Claparede,  "Les  tropismes  devant  la  psychologic, "  Journ.  f.  Psychologie  und 
Neurologie.  XIII,  150,  1908. 


52 


The  Mechanistic  Conception  of  Life 


the  harbor  at  Kiel,  when  brought  into  the  light  and  removed 
from  the  mud  shows  positive  heliotropism.  It  is,  therefore, 
just  as  incorrect  to  assert  that  the  heliotropic  reactions  are 

governed  by  the  bio- 
logical interests  of  the 
animal  as  that  this  is 
true  for  galvanotrop- 
ism.  We  must,  there- 
fore, free  ourselves  at 
once  from  the  over- 
valuation of  natural 
selection  and  accept 
the  consequences  of 
Mendel's  theory  of 
heredity,  according 
to  which  the  animal 
is  to  be  looked  upon 
as  an  aggregate  of  in- 
dependent hereditary 
qualities. 

VII 

The  attempt  has 
been  made  to  prove 
that  organisms  are 
attuned  to  a  certain 
intensity  of  light  and 
so  regulate  their 
heliotropism  that  they 
which  is  best  suited 
to  their  well-being.  I  believe  that  this  is  also  a  suggestion 
forced  upon  the  investigators  by  the  extreme  application 
of  the  iheory  of  natural  selection.  I  have  made  experi- 
ments  upon   a  large  number  of  animals,   but,   with  a  clear 


Fig.  21. — Arrangement  to  prove  that  posi- 
tively heliotropic  animals  move  toward  the  source 
of  light  even  if  by  so  doing  they  go  from  the  sun- 
light into  the  shade.  W  W  is  a,  window  through 
which  sunUght  S  falls  into  the  room.  By  a  piece 
of  board  d  e  the  sunlight  <S  is  prevented  from 
striking  the  region  6  c  of  a  table  near  the  window 
and  this  part  of  the  table  is  in  the  shade.  Only  the 
daylight  D  can  reach  this  part  of  the  table. 

A  test-tube  o  c  is  put  on  this  table  at  right 
angles  to  the  plane  of  the  window.  At  the  be- 
ginning of  the  experiment  the  animals  (e.g.,  the 
winged  aphides)  are  all  at  a.  The  animals  move 
at  once  toward  the  window,  but  instead  of  remain- 
ing at  b  they  keep  on  moving  from  the  direct 
sunlight  into  the  shade  toward  the  source  of  light 
until  they  all  reach  the  end  of  the  tube  c  near  the 
window  (in  the  shade)  where  they  remain  perma- 
nently. 


invariably  reach  that  intensity  of  light 


Significance  of  Tropisms  for  Psychology      53 

arrangement  of  the  physical  conditions  of  the  experiment,  I 
have  never  found  a  single  indication  of  such  an  adaptation. 
In  every  case  it  has  been  shown  that  positively  heliotropic 
animals  are  positive  to  any  intensity  of  light  above  the  threshold. 
Thus  winged  plant  lice  or  wingless  larvae  of  Chrysorrhoea  or 
copepods,  which  have  been  made  heliotropic  by  acids,  go  toward 
the  light  whether  the  source  of  light  is  the  direct  sunlight  or 
reflected  light  from  the  sky  or  weak  lamp  light,  provided  that 
the  (threshold)  value  of  the  intensity  of  light  required  for  the 
reaction  is  exceeded.  Indeed,  I  have  been  able  to  show  that 
positively  heliotropic  animals  also  move  toward  the  source  of 
light  even  if  the  arrangement  is  such  that  by  so  doing  they  go 
from  the  light  into  the  shadow.^  I  have  never  observed  a 
"selection"  of  a  suitable  intensity  of  light. 

What  probably  lies  behind  these  interpretations  of  the 
"selection  of  a  suitable  intensity  of  light"  is  the  fact  that  under 
certain  conditions  reaction  products  formed  by  the  photo- 
chemical action  of  light  may  inhibit  the  positive  heliotropism. 
I  found  a  very  clear  instance  of  this  sort  in  the  newly  hatched 
larvae  of  Balanus  perforatus,  which  are  positively  heliotropic. 
If  they  are  placed  in  the  light  of  a  quartz  mercury  lamp  (of 
Heraus),  which  is  very  rich  in  ultra-violet  rays,  the  positively 
heliotropic  larvae  soon  become  negatively  heliotropic.  For 
these  experiments  the  larvae  should  be  placed  only  in  a  very 
shallow  depth  of  sea-water. 

Even  in  a  strong  light  which  is  not  so  rich  in  ultra-violet 
rays  as  the  light  of  the  mercury  lamp,  it  is  sometimes  possible 
to  cause  positively  heliotropic  animals  to  become  negatively 
heliotropic.  This  is  the  case,  for  instance,  with  the  larvae  of 
Polygordius.  But  it  would  be  wrong  in  this  case  to  speak  of 
an  adaptation  of  the  animal  to  a  certain  intensity  of  light. 

1  Qiiite  often  without  even  stopping  for  a  moment.  In  animals  sensitive  to 
differences  (see  next  chapter)  a  stopping  occurs  in  this  experiment  in  the  passing 
from  the  light  into  the  shadow,  but  they  go,  nevertheless,  immediately  on  in  the 
direction  of  the  source  of  light.  The  reader  will  find  a  further  account  of  this 
experiment  in  my  book  on  The  Dynamics  of  Living  Matter. 


54  The  Mechanistic  Conception  of  Life 

In  my  opinion  it  is  merely  a  case  where  a  metabolic  product  either 
alters  the  photochemical  action  or  so  influences  the  central 
nervous  system  that  the  excitation  of  the  retina  by  the  light 
weakens  the  tonus  of  the  muscles,  instead  of  strengthening  it. 

Some  of  the  other  mistakes  have  perhaps  also  arisen  because 
the  writers  worked  with  complicated  experimental  conditions 
instead  of  with  simple  ones,  for  instance,  because  they  used  a 
hollow  prism  filled  with  ink  in  order  to  produce  a  gradual 
decrease  in  the  light  intensity.  In  the  semidarkness  thus  pro- 
duced, the  intensity  of  light  often  remains  beneath  or  near 
the  threshold  of  stimulation,  and  the  writers  fall  victims  to 
that  class  of  errors  which  we  have  already  pointed  out  in 
speaking  of  the  influence  of  lesser  intensities  of  light. 

VIII 
Heliotropic  phenomena  are  determined  by  the  relative 
rates  of  chemical  reactions  occurring  simultaneously  in  sym- 
metrical surface  elements  of  an  animal.  There  is  a  second  class 
of  phenomena  which  is  determined  by  a  sudden  change  in  the 
rate  of  chemical  reactions  in  the  same  surface  elements.  Reac- 
tions to  a  sudden  change  in  the  intensity  of  light  are  shown  most 
clearly  in  marine  tube-worms,  whose  gills  are  exposed  to  light. 
If  the  intensity  of  the  light  in  the  aquarium  is  suddenly  dimin- 
ished the  worms  withdraw  quickly  into  their  tubes.  A  sudden 
increase  in  the  intensity  of  light  has  no  such  effect.  With  other 
forms,  for  instance,  with  planarians,  a  sudden  decrease  in  the 
intensity  of  the  light  causes  a  decrease  in  movement.  Such  ani- 
mals gather  chiefly  in  parts  of  the  space  where  the  intensity  of 
light  is  relatively  small.  I  have  designated  such  reactions  as 
the  expression  of  sensitiveness  to  changes  in  the  intensity  of  a 
stimulus  C'Unterschiedsempfindlichkeit")  differential  sensi- 
bility, in  order  to  distinguish  them  from  tropisms.^ 

1  Loeb, "  Ueber  die  Umwandlung  positiv  heliotropischer  Tiere,  u.s.w.,"  Pflilgers 
Archiv,  1893.  See  also  the  recent  investigations  of  Georges  Bohn,  La  naissance  de 
V intelligence,  Paris,  1909;  "Les  essais  et  les  erreurs  chez  les  etioles  de  mer,"  Bull. 


Significance  of  Tropisms  for  Psychology      55 

It  is  hardly  necessary  to  point  out  here  that  the  effects  of 
rapid  changes  in  intensity,  when  they  are  very  marked,  can 
easily  complicate  and  entirely  obscure  the  heliotropic  phe- 
nomena. In  Hypotricha  and  other  infusoria  this  differential 
sensibility  is  very  pronounced  in  response  to  sudden  touch  or 
sudden  alteration  of  the  chemical  medium,  and  like  the  tube- 
worms  they  thereupon  draw  back  very  quickly.  Since  their 
locomotor  organs  are  not  symmetrical,  but  are  arranged  in  a 
peculiar  unsymmetrical  manner,  they  do  not,  after  the  next 
progressive  movement,  return  to  the  former  direction  of  move- 
ment, but  deviate  sideways  from  it,  and  it  is  therefore  easy 
to  understand  that  such  animals  do  not  furnish  the  best  ma- 
terial for  demonstrating  the  laws  of  heliotropism,  especially 
since  they  possess  only  a  slight  photochemical  sensitiveness. 
But  Jennings^  has  with  special  preference  used  observations  on 
such  organisms  to  argue  against  the  theory  of  tropisms.  Just 
as  the  action  of  a  constant  current  in  muscles  and  nerves  is 
different  from  that  of  an  intermittent  current,  so  we  find  an 
analogous  case  in  the  action  of  light.  If  we  wish  to  trace  all 
animal  reactions  back  to  physico-chemical  laws  we  must  take 
into  consideration  besides  the  tropisms  not  only  the  facts  of  the 
differential  sensibility  but  also  all  other  facts  which  exert  an 
influence  upon  the  reactions.  The  influence  of  that  mechanism 
which  we  call  "associative  memory"  also  belongs  in  this  cate- 
gory, but  we  cannot  discuss  this  further  at  this  place.  The 
reader  is  referred  to  my  book^  as  well  as  to  the  more  recent 
works  of  Bohn,  La  naissance  de  F intelligence^  and  La  nouvelle 
psychologie  animale.^     Let  us  bear  in  mind  that  ''ideas"  also 

Inst.  gen.  psychol.,  1907;    "Intervention  des  reactions  oscillatoires  dans  les  tro- 
pismes,"  Ass.  franc,  d.  Sciences,  1907. 

1  Jennings,  The  Behavior  of  Lower  Organisms,  1906. 

2  Comparative  Physiology  of  the  Brain  and  Comparative  Psychology,  New  York 
and  London,  1900. 

3  Paris,  "Bibliothequedephilosophiescientiflque,"  1909. 

<  Paris,  "  Bibliotheque  de  philosophie  contemporaine,"  1911. 


56  The  Mechanistic  Conception  of  Life 

can  act,  much  as  acids  do  for  the  heliotropism  of  certain 
animals,  namely,  to  increase  the  sensitiveness  to  certain  stimuli, 
and  thus  can  lead  to  tropism-like  movements  or  actions  directed 
toward  a  goal. 

IX 

Besides  light  and  the  electric  current,  the  force  of  gravity 
also  has  an  orienting  influence  upon  a  number  of  animals. 
The  majority  of  such  animals  are  forced  to  turn  their  heads 
away  from  the  center  of  the  earth  and  to  creep  upward.  It  was 
imcertain  for  a  long  time  how  the  orientation  of  cells  in  relation 
to  the  center  of  gravity  of  the  earth  could  influence  the  rate  of 
the  chemical  reactions  within,  but  it  has  been  suggested  that 
an  enlargement  or  shifting  of  the  reacting  surfaces  formed  the 
essential  connecting  link.  If  it  is  assumed  that  in  such  geo- 
tropically  sensitive  cells  two  phases  (for  instance,  two  fluid 
substances  which  are  not  at  all,  or  not  easily,  miscible,  or  one 
solid  and  one  fluid  substance)  of  different  specific  gravities  are 
present,  which  react  upon  one  another,  a  reaction  takes  place 
at  the  surfaces  of  contact.  Every  enlargement  of  the  latter  in- 
creases the  mass  of  reacting  molecules.  A  shifting  of  the  surfaces 
would  act  in  the  same  manner.  FinaJly,  a  third  possibility  re- 
mains which  could  perhaps  be  realized  in  plant  roots  and  stems. 
If  in  the  geotropically  sensitive  elements  two  masses  of  differ- 
ent specific  gravity  are  present,  only  one  of  which  reacts  to  the 
flowing  sap  in  the  center  or  the  periphery  of  the  stem,  the  cells 
of  the  upper  side  of  a  stem  which  is  laid  horizontally  will  ac- 
quire a  different  rate  of  reaction  from  those  of  the  lower  side, 
because  in  the  former  the  specifically  heavier  substances  are 
directed  toward  the  center  of  the  stem,  while  in  the  latter  the 
specifically  lighter  ones  are  directed  toward  the  center.  Con- 
sequently, one  side  will  grow  faster  than  the  other,  hence  the 
geotropic  bending.^  In  the  frog's  egg,  we  can  actually  demon- 
strate directly  the  existence  of  two   substances  of   different 

1  Chapter  on  "Tropisms"  in  Dynamics  of  Living  Matter. 


Significance  of  Tropisms  for  Psychology       57 

specific  gravity  and  can  study  their  behavior,  since  in  this  case 
they  are  of  different  color. 

In  animals  it  has  been  observed  that  orientation  toward  the 
center  of  gravity  of  the  earth  often  becomes  less  compulsory 
when  the  inner  ear  has  been  removed.  Mach  first  pointed 
out  the  possibility  that  the  otoliths  are  responsible  for  this. 
He  believed  that  they  might  press  upon  the  end-organs  of  the 
sensory  nerves  and  every  change  of  pressure  might  cause  a  cor- 
rection of  the  position  of  the  animal.  It  is  generally  assumed 
that  this  view  has  been  verified  by  experiment  but  I  cannot 
entirely  agree  with  it  although  I  once  described  experiments 
which  seemed  to  support  Mach's  otolith  theory.  I  had  found 
that  when  the  otoliths  of  the  inner  ear  of  the  shark  are  scraped 
out  with  a  sharp  spoon  the  normal  orientation  of  the  animal 
suffers;  but  if  the  otoliths  are  simply  washed  out  from  the 
inner  ear  by  a  weak  current  of  sea-water  the  orientation  does 
not  so  easily  suffer. 

In  the  latter  case,  it  is  doubtful  whether  all  the  otolith 
powder  has  been  removed  from  the  ear.  The  problem  was 
solved  by  experiments  on  flounders,  which  have  only  a  single 
large  otolith  that  can  easily  be  removed  from  the  ear.  E.  P. 
Lyon  carried  out  these  experiments,  which  showed  that  no 
disturbance  of  the  orientation  resulted  from  this  operation.  We 
may  conclude,  therefore,  that  in  my  experiments  of  scraping 
out  the  otoliths  a  distm-bance  of  the  orientation  occurred, 
because  in  so  doing  the  nerve  endings  in  the  ears  were  injured. 
We  have,  therefore,  no  right  to  maintain  that  the  orientation  of 
animals  in  relation  to  the  center  of  gravity  of  the  earth  is  regu- 
lated by  the  pressure  of  the  otoliths  upon  the  nerve  endings, 
but  that  this  regulation  takes  place  in  the  nerve  endings  them- 
selves, and  probably,  indeed,  as  a  result  of  the  existence  there 
of  two  different  phases  of  different  specific  gravity  which  react 
upon  one  another.  Through  the  change  of  orientation  of  the 
cells  in  relation  to  the  center  of  gravity  of  the  earth,  the  two 


58  The  Mechanistic  Conception  of  Life 

phases  undergo  a  shifting  by  means  of  which  a  change  in  the 
rate  of  reaction  is  brought  about  according  to  one  of  the  ways 
described  above.  Since  then  I  have  looked  through  the  litera- 
ture on  the  function  of  the  otoliths  or  statoliths,  and  have 
reached  the  conclusion  that  all  writers  who  assert  that  the 
removal  of  the  otoliths  disturbs  the  geotropic  orientation  of 
animals  have  been  victims  of  the  same  fallacy  as  myself.  They 
have  injured  or  removed  the  nerve  endings.  In  the  only  case 
in  which  a  removal  of  the  otoliths  without  tearing  or  other 
injury  of  the  nerve  endings  can  be  justifiably  assumed,  no  dis- 
turbance of  the  orientation  occurred. 

While  in  my  own  work  I  have  aimed  to  trace  the  complex 
reactions  of  animals  back  to  simpler  reactions  like  those  of 
plants  and  finally  to  physico-chemical  laws,  the  opposite 
tendency  has  lately  been  gaining  influence.  Some  botanists, 
namely,  Haberlandt,  Nemec,  and  F.  Darwin,  endeavor  to  show 
that  the  relatively  simpler  reactions  of  plants  may  be  traced 
back  to  the  more  complex  relations  found  in  animals.  Instead 
of  deriving  the  tropic  reactions  of  plants  as  directly  as  possible 
from  the  law  of  mass  action  or  the  law  of  Bunsen  and  Roscoe, 
they  try  to  show  that  "sense-organs''  exist  in  the  cells  of 
plants  and  France  even  attributes  to  the  latter  a  "soul"  and 
"intelligence."  I  believe  that  in  order  to  be  consistent,  these 
writers  ought  to  base  the  law  of  mass  action  upon  the  assump- 
tion of  the  existence  of  sense-organs,  souls,  and  intelligence  in 
the  molecules  and  ions.  It  is  probably  unnecessary  to  empha- 
size the  fact  that  it  is  better  for  the  progress  of  science  to  derive 
the  more  complex  phenomena  from  simpler  components  than  to 
do  the  contrary.  For  all  "explanation"  consists  solely  in  the 
presentation  of  a  phenomenon  as  an  unequivocal  function  of 
the  variables  by  which  it  is  determined,  and  if  in  nature  we  find 
a  function  of  two  variables,  it  does  not,  in  my  opinion,  tend 
toward  progress  to  assert  that  this  is  a  case  of  functions  of 
more  than  two  variables,  without  furnishing  sufficient  proof  for 
this  assertion. 


Significance  of  Tropisms  for  Psychology      59 

These  writers  explain  the  geotropic  reactions  of  plants 
by  saying  that  in  certain  cells  starch  grains  are  present  which 
serve  the  purpose  of  the  otoliths  in  animals.  These  starch 
grains  are  believed  to  press  upon  the  sense-organs  or  nerve 
endings  in  the  plant  cells  concerned  and  the  "pressure-sense" 
of  the  plant  is  then  supposed  to  give  rise  to  the  geotropic  curva- 
ture. I  have  no  opposition  to  offer  to  the  assumption  that  the 
starch  grains  change  their  position  with  a  change  in  the  position 
of  the  cells,  and  I  am  also  willing  to  pass  over  for  the  present 
the  view  that  the  starch  grains  form  one  of  the  two  phases  in 
the  cell.  But  I  see  no  necessity  for  assuming  besides  this 
the  existence  of  intracellular  sense-organs  which  perceive  the 
pressure  of  the  starch  grains.  This  is,  in  my  opinion,  an 
unnecessary  complication  of  simple  relations. 

X 

The  progress  of  natural  science  depends  upon  the  dis- 
covery of  rationalistic  elements  or  simple  natural  laws.  We 
find  that  there  are  two  classes  of  investigators  in  biology, 
grouped  according  to  their  attitude  toward  such  simple  laws 
or  rationalistic  elements.  One  seems  to  aim  at  the  denial  of 
the  existence  of  such  simple  laws  and  every  new  case  which 
does  not  fall  at  once  under  such  a  law  offers  an  opportunity 
for  them  to  point  out  the  inadequacy  of  the  latter.  The  other 
group  of  investigators  aims  to  discover  and  not  to  disprove 
laws.  When  such  investigators  have  discovered  a  simple  law 
which  is  generally  applicable,  they  know  that  an  apparent 
exception  does  not  necessarily  overthrow  the  law,  but  that 
possibly  an  opportunity  is  offered  for  a  new  discovery  and  an 
extension  of  the  old  law.  Mendel's  laws  have  been  brilliantly 
confirmed  in  a  number  of  cases.  In  some  cases  of  apparent 
deviations  (from  these  laws),  however,  it  has  not  always  been 
possible  at  once  to  recognize  the  cause.  One  group  of  investi- 
gators has  recognized  that  these  deviations  do  not  indicate  the 
incorrectness  of  Mendel's  laws,  but  that  they  are  merely  the 


60  The  Mechanistic  Conception  of  Life 

result  of  secondary  and  often  minor  complications ;  the  latter 
investigators  have  from  this  standpoint  made  further  fruitful 
discoveries.  The  role  of  the  other  group  of  investigators  in 
this  case  has  consisted,  primarily,  in  an  attempt  to  minimize 
the  importance  of  Mendel's  laws  and  thus  to  retard  the  progress 
of  science. 

The  case  is  similar  in  the  realm  of  tropisms.  Tropisms 
and  tropism-like  reactions  are  elements  which  pave  the  way 
for  a  rationalistic  conception  of  the  psychological  reactions  of 
animals  and  I  believe,  therefore,  that  it  is  in  the  interest  of  the 
progress  of  science  to  develop  further  the  theory  of  animal 
tropisms.  The  fact  that  in  an  electric  current  the  same  animal 
often  moves  differently  from  what  it  does  under  the  influence 
of  light  finds  its  explanation  for  the  observer  conversant  with 
physical  chemistry  in  the  fact  that  the  electric  current  causes 
changes  in  the  concentration  of  ions  within,  as  well  as  upon  the 
surface,  while  the  chemical  action  of  light  is  essentially  limited 
to  the  surface.  Certain  writers,  however,  leave  this  difference 
in  the  action  of  the  two  agents  out  of  consideration  and  make 
use  of  the  difference  in  the  behavior  of  certain  organisms  in 
response  to  light  and  to  the  electric  current,  to  assert  that  it 
is  not  permissible  to  speak  of  tropisms  as  being  governed 
by  general  laws;  in  other  words,  they  say  that  tropisms  are 
without  significance.  Animals  in  general  are  symmetrically 
built  and  the  motor  elements  of  the  right  and  left  sides  of  the 
body  usually  act  symmetrically.  Consequently  the  heliotropic 
orientation,  for  instance,  comes  about  as  we  have  already 
described.  There  are  animals,  however,  which  move  sideways, 
for  instance,  certain  crabs,  such  as  the  fiddler  crab.  Holmes 
has  found  that  these  crustaceans  also  go  sideways  toward  the 
light.  Jennings  draws  from  this  fact  the  following  conclusions: 
"The  symmetrical  position  is  an  incident  of  the  reaction,  not 
its  essence." 

In  other  words,  he  uses  these  observations  of  Holmes  to 


Significance  of  Tropisms  for  Psychology      61 

indicate  that  the  role  ascribed  to  symmetry  has  no  importance 
for  the  theory  of  tropisms.  I  am,  however,  inclined  to  draw 
another  conclusion,  namely,  that  in  the  fiddler  crabs  in  the 
first  place  there  is  an  entirely  different  connection  between  the 
retina  and  the  locomotor  muscles  from  that  in  other  crustaceans, 
and  that,  secondly,  there  is  a  special  peculiarity  in  regard  to 
the  function  of  the  two  retinae  whereby  they  do  not  act  like 
symmetrical  surface  elements.  I  believe  that  a  new  discovery 
may  be  made  here.^ 

XI 

These  data  may  suffice  to  explain  my  point  of  view.  To  me 
it  is  a  question  of  making  the  facts  of  psychology  accessible 
to  analysis  by  means  of  physical  chemistry.  In  this  way  it  is 
already  possible  to  reduce  a  set  of  reactions,  namely,  the  tro- 
pisms to  simple  rationalistic  relations.  Many  animals,  because 
their  body  structure  is  not  only  morphologically,  but  also 
chemically,  symmetrical,  are  obliged  to  orient  their  bodies  in 
a  certain  way  in  relation  to  certain  centers  of  force,  as,  for  in- 
stance, the  course  of  light,  an  electric  current,  the  center  of 
gravity  of  the  earth,  or  chemical  substances.  This  orientation 
is  automatically  regulated  according  to  the  law  of  mass  action. 
The  application  of  the  law  of  mass  action  to  this  set  of  reactions 
is  thus  made  possible.  I  consider  it  unnecessary  to  give  up 
the  term  "comparative  psychology,"  but  I  am  of  the  opinion 
that  the  contents  of  comparative  psychology  will  under  the 
influence  of  the  above-mentioned  endeavors  be  different  from 
the  contents  of  speculative  psychology.  But  I  believe  also 
that  the  further  development  of  this  subject  will  fall  more  to 
the  lot  of  biologists  trained  in  physical  chemistry  than  to  the 
specialists  in  psychology  or  zoology,  for  it  is  in  general  hardly 

1  From  which  I  expect,  furthermore,  that  they  will  only  confirm  still  more 
the  laws  of  heliotropism.  This  expectation  is  based  upon  analogous  relations  in 
the  pleuronectids,  which  I  cannot,  however,  discuss  further  here.  However, 
probably  no  one  will  maintain  that  the  existence  of  the  pleuronectids  invahdatea 
all  laws  in  regard  to  the  symmetrical  body  structure. 


62  The  Mechanistic  Conception  of  Life 

to  be  expected  that  zoologists  and  psychologists  who  lack  a 
physico-chemical  training  will  feel  attracted  to  the  subject  of 
tropisms. 

In  closing  let  me  add  a  few  remarks  concerning  the  possible 
application  of  the  investigations  of  tropisms. 

I  believe  that  the  investigation  of  the  conditions  which 
produce  tropisms  may  be  of  importance  for  psychiatry.  If  we 
can  call  forth  in  an  animal  otherwise  indifferent  to  light  by 
means  of  an  acid  a  heliotropism  which  drives  it  irresistibly  into 
a  flame;  if  the  same  thing  can  be  brought  about  by  means  of  a 
secretion  of  the  reproductive  glands,  we  have  given,  I  believe, 
a  group  of  facts,  within  which  the  analogies  necessary  for 
psychiatry  can  be  called  forth  experimentally  and  can  be 
investigated. 

These  experiments  may  also  attain  a  similar  value  for 
ethics.  The  highest  manifestation  of  ethics,  namely,  the  con- 
dition that  human  beings  are  willing  to  sacrifice  their  lives  for 
an  idea  is  comprehensible  neither  from  the  utilitarian  stand- 
point nor  from  that  of  the  categorical  imperative.  It  might  be 
possible  that  under  the  influence  of  certain  ideas  chemical 
changes,  for  instance,  internal  secretions  within  the  body,  are 
produced  which  increase  the  sensitiveness  to  certain  stimuli  to 
such  an  unusual  degree  that  such  people  become  slaves  to  cer- 
tain stimuli  just  as  the  copepods  become  slaves  to  the  light 
when  carbon  dioxide  is  added  to  the  water.  Since  Pawlow 
and  his  pupils  have  succeeded  in  causing  the  secretion  of  saliva 
in  the  dog  by  means  of  optic  and  acoustic  signals,  it  no  longer 
seems  strange  to  us  that  what  the  philosopher  terms  an  ''idea" 
is  a  process  which  can  cause  chemical  changes  in  the  body. 


III.  SOME  FUNDAMENTAL  FACTS  AND  CONCEP- 
TIONS CONCERNING  THE  COMPARATIVE  PHYS- 
IOLOGY OF  THE   CENTRAL  NERVOUS  SYSTEM 


Ill 

SOME  FUNDAMENTAL  FACTS  AND  CONCEPTIONS  CON- 
CERNING  THE    COMPARATIVE   PHYSIOLOGY 
OF  THE  CENTRAL  NERVOUS  SYSTEM  ^ 

1.  The  understanding  of  complicated  phenomena  depends 
upon  an  analysis  by  which  they  are  resolved  into  their  simple 
elementary  components.  If  we  ask  what  the  elementary  com- 
ponents are  in  the  physiology  of  the  central  nervous  system, 
our  attention  is  directed  to  a  class  of  processes  which  are  called 
reflexes.  A  reflex  is  a  reaction  which  is  caused  by  an  external 
stimulus,  and  which  results  in  a  coordinated  movement,  the 
closing  of  the  eyelid,  for  example,  when  the  conjuctiva  is 
touched  by  a  foreign  body,  or  the  narrowing  of  the  pupil  under 
the  influence  of  light.  In  each  of  these  cases,  changes  in  the 
sensory  nerve  endings  are  produced  which  bring  about  a  change 
of  condition  in  the  nerves.  This  change  travels  to  the  central 
nervous  system,  passes  from  there  to  the  motor  nerves,  and 
terminates  in  the  muscle-fibers,  producing  there  a  contraction. 
This  passage  from  the  stimulated  part  to  the  central  nervous 
system,  and  back  again  to  the  peripheral  muscles,  is  called  a 
reflex.  There  has  been  a  growing  tendency  in  physiology  to 
make  reflexes  the  basis  of  the  analysis  of  the  functions  of  the 
central  nervous  system,  and  consequently  much  importance 
has  been  attached  to  the  processes  underlying  them  and  the 
mechanisms  necessary  for  reflex. 

The  name  reflex  suggests  a  comparison  between  the  spinal 
cord  and  a  mirror.  Sensory  stimuli  were  supposed  to  be 
reflected  from  the  spinal  cord  to  the  muscles;  destruction  of  the 
spinal  cord  would,  according  to  this,  make  the  reflex  impossible, 

^  Reprinted  from  Loeb,  J.,  Comparative  Physiology  of  the  Brain  and  Compara- 
tive Psychology  (1899).  By  courtesy  of  G.  P.  Putnam's  Sons  of  New  York  and 
London. 

65 


66  The  Mechanistic  Conception  of  Life 

just  as  the  destruction  of  the  mirror  might  prevent  the  reflection 
of  light.  This  comparison,  however,  of  the  reflex  process  in 
the  central  nervous  system  with  the  reflection  of  light  has, 
long  since,  become  meaningless,  and  at  present  few  physiologists 
in  using  the  term  reflex  think  of  its  original  significance.  In- 
stead of  this,  another  feature  in  the  conception  of  the  term 
reflex  has  gained  prominence,  namely,  the  purposeful  character 
of  many  reflex  movements.  The  closing  of  the  eyelid  and  the 
narrowing  of  the  pupil  are  eminently  purposeful,  for  the  cornea 
is  thereby  protected  from  hurtful  contact  with  foreign  bodies, 
and  the  retina  from  the  injurious  effects  of  strong  light. 
Another  striking  characteristic  in  such  reflexes  has  also  been 
emphasized.  The  movements  which  are  produced  are  so  well 
planned  and  coordinated  that  it  seems  as  though  some  intelli- 
gence were  at  work  either  in  devising  or  in  carrying  them  out. 
The  fact,  however,  that  even  a  decapitated  frog  will  brush 
with  its  foot  a  drop  of  acetic  acid  from  its  skin,  suggests  that 
some  other  explanation  is  necessary.  A  prominent  psychologist 
has  maintained  that  reflexes  are  to  be  considered  as  the  mechani- 
cal effects  of  acts  of  volition  of  past  generations.^  The  ganglion- 
cell  seems  the  only  place  where  such  mechanical  effects  could 
be  stored  up.  It  has  therefore  been  considered  the  most 
essential  element  of  the  reflex  mechanism,  the  nerve-fibers 
being  regarded,  and  probably  correctly,  merely  as  conductors. 

Both  the  authors  who  emphasize  the  purposefuhiess  of  the 
reflex  act  and  those  who  see  in  it  only  a  physical  process  have 
invariably  looked  upon  the  ganglion-cell  as  the  principal  bearer 
of  the  structures  for  the  complex  coordinated  movements  in 
reflex  action. 

I  should  have  been  as  little  inclined  as  any  other  physiolo- 
gist to  doubt  the  correctness  of  this  conception  had  not  the 
establishment  of  the  identity  of  the  reactions  of  animals  and 
plants  to  light  proved  the  untenability  of  this  view  and  at  the 

1  A  statement  for  which  no  trace  of  experimental  proof  exists. 


Physiology  of  Central  Nervous  System        67 

same  time  offered  a  different  conception  of  reflexes.  The  flight 
of  the  moth  into  the  flame  is  a  typical  reflex  process.  The 
light  stimulates  the  peripheral  sense-organs,  the  stimulus  passes 
to  the  central  nervous  system,  and  from  there  to  the  muscles  of 
the  wings,  and  the  moth  is  caused  to  fly  into  the  flame.  This 
reflex  process  agrees  in  every  point  with  the  heliotropic  effects 
of  light  on  plant  organs.  Since  plants  possess  no  nerves  and  no 
ganglia,  this  identity  of  animal  with  plant  heliotropism  can 
force  but  one  inference — these  heliotropic  effects  must  depend 
upon  conditions  which  are  common  to  both  animals  and  plants. 
At  the  end  of  my  book  on  heliotropism^  I  expressed  this  view 
in  the  following  words:  "We  have  seen  that,  in  the  case  of 
animals  which  possess  nerves,  the  movements  of  orientation 
toward  light  are  governed  by  exactly  the  same  external  condi- 
tions, and  depend  in  the  same  way  upon  the  external  form  of  the 
body,  as  in  the  case  of  plants  which  possess  no  nerves.  These 
heliotropic  phenomena,  consequently,  cannot  depend  upon 
specific  qualities  of  the  central  nervous  system."  On  the  other 
hand,  the  objection  has  been  raised  that  destruction  of  the 
ganglion-cells  interrupts  the  reflex  process.  This  argument, 
however,  is  not  sound,  for  the  nervous  reflex  arc  in  higher  animals 
forms  the  only  protoplasmic  bridge  between  the  sensory  organs 
of  the  surface  of  the  body  and  the  muscles.  If  we  destroy 
the  ganglion-cells  or  the  central  nervous  system,  we  interrupt 
the  continuity  of  the  protoplasmic  conduction  between  the 
surface  of  the  body  and  the  muscles,  and  a  reflex  is  no  longer 
possible.  Since  the  axis  cylinders  of  the  nerves  and  the 
ganglion-cells  are  nothing  more  than  protoplasmic  formations, 
we  are  justifled  in  seeking  in  them  only  general  protoplasmic 
qualities,  unless  we  find  that  the  phenomena  cannot  be  explained 
by  means  of  the  latter  alone. 

2.  A  further  objection  has  been  raised,  that  although  these 

1  Loeb,  J.,  Der  Heliotropismus  der  Tiere  und  seine  U ebereinstimmung  mit  dem 
Heliotropismus  der  Pflanzen,  Wiirzburg,  1890.  A  preliminary  note  on  these 
experiments  appeared  January,  1888. 


68  The  Mechanistic  Conception  of  Life 

reflexes  occur  in  plants  possessing  no  nervous  system,  yet  in 
animals  where  ganglion-cells  are  present  the  very  existence  of 
the  ganglion-cells  necessitates  the  presence  in  them  of  special 
reflex  mechanisms.  It  was  therefore  necessary  to  find  out  if 
there  were  not  animals  in  which  coordinated  reflexes  still  con- 
tinued to  exist  after  the  destruction  of  the  central  nervous 
system.  Such  a  phenomenon  could  be  expected  only  in  forms 
in  which  a  direct  transmission  of  stimuli  from  the  skin  to  the 
muscle  or  direct  stimulation  of  the  muscle  is  possible,  in  addi- 
tion to  the  transmission  through  the  reflex  arc.  This  is  the 
case,  for  instance,  in  worms  and  in  ascidians.  I  succeeded^  in 
demonstrating  in  Ciona  intestinalis  that  the  complicated  reflexes 
still  continue  after  removal  of  the  central  nervous  system.^ 

A  study,  then,  of  comparative  physiology  brings  out  the 
fact  that  irritability  and  conductibility  are  the  only  qualities 
essential  to  reflexes,  and  these  are  both  common  qualities  of 
all  protoplasm.  The  irritable  structures  at  the  surface  of  the 
body,  and  the  arrangement  of  the  muscles  determine  the 
character  of  the  reflex  act.  The  assumption  that  the  central 
nervous  system  or  the  ganglion-cells  are  the  specific  bearers  of 
reflex  mechanisms  cannot  hold.  But  have  we  now  to  conclude 
that  the  nerves  are  superfluous  and  a  waste  ?  Certainly  not. 
Their  value  lies  in  the  fact  that  they  are  quicker  and  more 
sensitive  conductors  than  undifferentiated  protoplasm.  Because 
of  these  qualities  of  the  nerves,  an  animal  is  better  able  to  adapt 
itself  to  changing  conditions  than  it  possibly  could  if  it  had  no 
nerves.  Such  power  of  adaptation  is  absolutely  necessary  for 
free  animals. 

3.  While  some  authors  explain  all  reflexes  on  a  psychical 
basis,  the  majority  of  investigators  explain  in  this  way  only  a 

1  Loeb,  J.,  Untersuchungen  zur  physiologischen  Morphologie  der  Tiere,  II, 
WiiTzburg,  1892. 

2  This  animal  closes  the  oral  opening  when  we  touch  it.  This  is  a  reflex  com- 
parable to  the  closing  of  the  eyelid  if  we  touch  the  cornea.  The  central  nervous 
sytem  of  the  animal  consists  of  one  ganglion.  When  the  latter  is  removed  the 
oral  opening  still  closes  upon  mechanical  stimulation. 


Physiology  of  Central  Nervous  System        69 

certain  group  of  reflexes — ^the  so-called  instincts.  Instincts 
are  defined  in  various  ways,  but  no  matter  how  the  definition 
is  phrased  the  meaning  seems  to  be  that  they  are  inherited 
reflexes  so  purposeful  and  so  complicated  in  character  that 
nothing  short  of  intelligence  and  experience  could  have  produced 
them.  To  this  class  of  reflexes  belongs  the  habit  possessed  by 
certain  insects  of  laying  their  eggs  on  the  material  which  the 
larvae  will  afterward  require  for  food.  When  we  consider  that 
the  female  fly  pays  no  attention  to  her  eggs  after  laying  them, 
we  cannot  cease  to  wonder  at  the  seeming  care  which  nature 
takes  for  the  preservation  of  the  species.  How  can  the  action 
of  such  an  insect  be  determined  if  not  by  mysterious  structures 
which  can  only  be  contained  in  the  ganglion-cells  ?  How  can  we 
explain  the  inheritance  of  such  instincts  if  we  believe  it  to  be  a 
fact  that  the  ganglion-cells  are  only  the  conductors  of  stimuli  ? 
It  was  impossible  either  to  develop  a  mechanics  of  instincts  or 
to  explain  their  inheritance  in  a  simple  way  from  the  old  stand- 
point, but  our  conception  makes  an  explanation  possible. 
Among  the  elements  which  compose  these  complicated  instincts, 
the  tropisms  (heliotropism,  chemotropism,  geotropism,  stere- 
otropism)  play  an  important  part.  These  tropisms  are  identical 
for  animals  and  plants.  The  explanation  of  them  depends  first 
upon  the  specific  irritability  of  certain  elements  of  the  body- 
surface,  and,  second,  upon  the  relations  of  symmetry  of  the 
body.  Symmetrical  elements  at  the  surface  of  the  body  have 
the  same  irritability;  unsymmetrical  elements  have  a  different 
irritability.  Those  nearer  the  oral  pole  possess  an  irritability 
greater  than  that  of  those  near  the  aboral  pole.  These  circum- 
stances force  an  animal  to  orient  itself  toward  a  source  of  stimu- 
lation in  such  a  way  that  symmetrical  points  on  the  surface 
of  the  body  are  stimulated  equally.  In  this  way  the  animals 
are  led  without  will  of  their  own  either  toward  the  source  of 
the  stimulus  or  away  from  it.  Thus  there  remains  nothing 
for  the  ganglion-cell  to  do  but  to  conduct  the  stimulus,  and 


70  The  Mechanistic  Conception  of  Life 

this  may  be  accomplished  by  protoplasm  in  any  form.  For 
the  inheritance  of  instincts  it  is  only  necessary  that  the  egg 
contain  certain  substances — which  will  determine  the  different 
tropisms — and  the  conditions  for  producing  bilateral  symmetry 
of  the  embryo.  The  mystery  with  which  the  ganglion-cell  has 
been  surrounded  led  not  only  to  no  definite  insight  into  these 
processes,  but  has  proved  rather  a  hindrance  in  the  attempt  to 
find  the  explanation  of  them. 

It  is  evident  that  there  is  no  sharp  line  of  demarkation 
between  reflexes  and  instincts.  We  find  that  authors  prefer 
to  speak  of  reflexes  in  cases  where  the  reaction  of  single  parts 
or  organs  of  an  animal  to  external  stimuli  is  concerned;  while 
they  speak  of  instincts  where  the  reaction  of  the  animal  as  a 
whole  is  involved  (as  is  the  case  in  tropisms). 

4.  If  the  mechanics  of  a  number  of  instincts  is  explained 
by  means  of  the  tropisms  common  to  animals  and  plants,  and 
if  the  significance  of  the  ganglion-cells  is  confined,  as  in  all 
reflex  processes,  to  their  power  of  conducting  stimuli,  we  are 
forced  to  ask  what  circumstances  determine  the  coordinated 
movements  in  reflexes,  especially  in  the  more  complicated  ones. 
The  assumption  of  complicated  but  unknown  and  perhaps 
unknowable  structures  in  the  ganglion-cells  served  formerly  as 
a  convenient  terminus  for  all  thought  in  this  direction.  In 
giving  up  this  assumption,  we  are  called  upon  to  show  what 
conditions  are  able  to  determine  the  coordinated  character  of 
reflex  movements.  Experiments  on  galvanotropism  of  animals 
suggest  that  a  simple  relation  may  exist  between  the  orientation 
of  certain  motor  elements  in  the  central  nervous  system  and 
the  direction  of  the  movements  of  the  body  which  is  called 
forth  by  the  activity  of  these  elements.  This  perhaps  creates 
a  rational  basis  for  the  further  investigation  of  coordinated 
movements.^ 

1  Since  this  was  written  von  UexkueU  found  a  law  which  will  go  far  in  explaining 
the  mechanism  of  coordination,  namely,  that  a  stretched  muscle  shows  an  increased 
irritability  while  the  contracted  muscle  shows  a  decreased  irritability.     Since 


Physiology  of  Central  Nervous  System        71 

5.  We  must  also  deprive  the  ganglion-cells  of  all  specific 
significance  in  spontaneous  movements,  just  as  we  have  done 
in  the  case  of  simple  reflexes  and  instincts.  By  spontaneous 
movements  we  mean  movements  which  are  apparently  deter- 
mined by  internal  conditions  of  the  living  system.  Strictly 
speaking,  no  movements  of  animals  are  exclusively  determined 
by  internal  conditions,  for  atmospheric  oxygen  and  a  certain 
range  of  temperature  are  always  necessary  in  order  to  preserve 
the  activity  beyond  a  short  period  of  time. 

We  must  discriminate  between  simple  and  conscious  spon- 
taneity. In  simple  spontaneity  we  must  consider  two  kinds 
of  processes,  namely,  aperiodic  spontaneous  processes  and 
rhythmically  spontaneous  or  automatic  processes.  The  rhyth- 
mical processes  are  of  importance  for  our  consideration. 
Respiration  and  the  heart  beat  belong  in  this  category.  The 
respiratory  movements  seem  to  indicate  that  automatic 
activity  can  arise  in  the  ganglion-cells,  and  from  this  the  con- 
clusion has  been  drawn  that  all  automatic  movements  are  due 
to  specific  structures  of  the  ganglion-cells.  Recent  investiga- 
tions, however,  have  transferred  the  problem  of  rhythmical 
spontaneous  contractions  from  the  field  of  morphology  into  that 
of  physical  chemistry.  The  peculiar  qualities  of  each  tissue  are 
partly  due  to  the  fact  that  it  contains  certain  ions  (Na,  K,  Ca, 
and  others)  in  definite  proportions.  By  changing  these  pro- 
portions, we  can  impart  to  a  tissue  properties  which  it  does  not 
ordinarily  possess.  If  in  the  muscles  of  the  skeleton  the  Na 
ions  be  increased  and  the  Ca  ions  be  reduced,  the  muscles  are 
able  to  contract  rhythmically  like  the  heart.  It  is  only  the 
presence  of  Ca  ions  in  the  blood  which  prevents  the  muscles 
of  our  skeleton  from  beating  rhythmically  in  our  body.  As  the 
muscles  contain  no  ganglion-cells,  it  is  certain  that  the  power  of 
rhythmical  spontaneous  contractions  is  not  due  to  the  specific 

the  contraction  of  one  group  of  muscles  necessitates  the  stretching  of  their  antago- 
nists the  coordinated  character  of  locomotive  action  seems  to  become  intelligible 
(1912). 


72  The  Mechanistic  Conception  of  Life 

morphological  character  of  the  ganglion-cells,  but  to  definite 
chemical  conditions  which  are  not  necessarily  confined  to 
ganglion-cells.^ 

The  coordinated  character  of  automatic  movements  has 
often  been  explained  by  the  assumption  of  a  ''center  of  coordina- 
tion," which  is  supposed  to  keep  a  kind  of  police  watch  on  the 
different  elements  and  see  that  they  move  in  the  right  order. 
Observations  in  lower  animals,  however,  show  that  the  coordina- 
tion of  automatic  movements  is  caused  by  the  fact  that  that 
element  which  beats  most  quickly  forces  the  others  to  beat  in 
its  own  rhythm.  Aperiodic  spontaneity  is  still  less  a  specific 
function  of  the  ganglion-cell  than  rhythmical  spontaneity.  The 
swarm  spores  of  algae,  which  possess  no  ganglion-cells,  show 
spontaneity  equal  to  that  of  animals  having  ganglion-cells. 

6.  Thus  far  we  have  not  touched  upon  the  most  important 
problem  in  physiology,  namely,  which  mechanisms  give  rise 
to  that  complex  of  phenomena  which  are  called  psychic  or 
conscious.  Our  method  of  procedure  must  be  the  same  as  in 
the  case  of  instincts  and  reflexes.  We  must  find  out  the  ele- 
mentary physiological  processes  which  underlie  the  complicated 
phenomena  of  consciousness.  Some  physiologists  and  psy- 
chologists consider  the  purposefulness  of  the  psychic  action 
as  the  essential  element.  If  an  animal  or  an  organ  reacts  as  a 
rational  human  being  would  do  under  the  same  circumstances, 
these  authors  declare  that  we  are  dealing  with  a  phenomenon  of 
consciousness.  In  this  way  many  reflexes,  the  instincts 
especially,  are  looked  upon  as  psychic  functions.  Conscious- 
ness has  been  ascribed  even  to  the  spinal  cord,  because  many  of 
its  functions  are  purposeful.  We  shall  see  in  the  following 
chapters  that  many  of  these  reactions  are  merely  tropisms 
which  may  occur  in  exactly  the  same  form  in  plants.  Plants 
must  therefore  have  a  psychic  life,  and,  following  the  argument, 
we  must  ascribe  it  to  machines  also,  for  the  tropisms  depend 

1  Loeb,  J.,  American  Journal  of  Physiology,  III,  327  and  383,  1900. 


Physiology  of  Central  Nervous  System        73 

only  on  simple  mechanical  arrangements.  In  the  last  analysis, 
then,  we  would  arrive  at  molecules  and  atoms  endowed  with 
mental  qualities.  We  can  dispose  of  this  view  by  the  mere  fact 
that  the  phenomena  of  embryological  development  and  of 
organization  in  general  show  a  degree  of  purposefulness  which 
may  even  surpass  that  of  any  reflex  or  instinctive  or  conscious 
act.  And  yet  we  do  not  consider  the  phenomena  of  develop- 
ment to  be  dependent  upon  consciousness. 

On  the  other  hand,  physiologists  who  have  appreciated  the 
untenable  character  of  such  metaphysical  speculations  have 
held  that  the  only  alternative  is  to  drop  the  search  for  the 
mechanisms  underlying  consciousness  and  study  exclusively  the 
results  of  operations  on  the  brain.  This  would  be  throwing 
out  the  \Aheat  with  the  chaff.  The  mistake  made  by  meta- 
physicians is  not  that  they  devote  themselves  to  fundamental 
problems,  but  that  they  employ  the  wrong  methods  of  investi- 
gation and  substitute  a  play  on  words  for  an  explanation  by 
means  of  facts.  If  brain  physiology  gives  up  its  fundamental 
problem,  namely,  the  discovery  of  those  elementary  processes 
which  make  consciousness  possible,  it  abandons  its  best  possi- 
bilities. But  to  obtain  results,  the  errors  of  the  metaphysician 
must  be  avoided  and  explanations  must  rest  upon  facts,  not 
words.  The  method  should  be  the  same  for  animal  psychology 
that  it  is  for  brain  physiology.  It  should  consist  in  the  right 
understanding  of  the  fundamental  process  which  recurs  in 
all  psychic  phenomena  as  the  elemental  component.  This 
process,  according  to  my  opinion,  is  the  activity  of  the  associative 
memory,  or  of  association.  Consciousness  is  only  a  metaphysical 
term  for  phenomena  which  are  determined  by  associative 
memory.  By  associative  memory  I  mean  that  mechanism  by 
which  a  stimulus  brings  about  not  only  the  effects  which  its 
nature  and  the  specific  structure  of  the  irritable  organ  call  for, 
but  by  which  it  brings  about  also  the  effects  of  other  stimuli 
which   formerly   acted   upon   the   organism   almost   or    quite 


74  The   Mechanistic  Conception  of  Life 

simultaneously  with  the  stimulus  in  question.^  If  an  animal 
can  be  trained,  if  it  can  learn,  it  possesses  associative  memory. 
By  means  of  this  criterion  it  can  be  shown  that  Infusoria, 
Coelenterates,  and  worms  do  not  possess  a  trace  of  associative 
memory.  Among  certain  classes  of  insects  (for  instance,  ants, 
bees,  and  wasps),  the  existence  of  associative  memory  can  be 
proved.  It  is  a  comparatively  easy  task  to  find  out  which 
representatives  of  the  various  classes  of  animals  possess,  and 
which  do  not  possess,  associative  memory.  Our  criterion 
therefore  might  be  of  great  assistance  in  the  development  of 
comparative  psychology. 

7.  Our  criterion  puts  an  end  to  the  metaphysical  ideas  that 
all  matter,  and  hence  the  whole  animal  world,  possesses  con- 
sciousness. We  are  brought  to  the  theory  that  only  certain 
species  of  animals  possess  associative  memory  and  have  con- 
sciousness, and  that  it  appears  in  them  only  after  they  have 
reached  a  certain  stage  in  their  ontogenetic  development.  This 
is  apparent  from  the  fact  that  associative  memory  depends 
upon  mechanical  arrangements  which  are  present  only  in  certain 
animals,  and  present  in  these  only  after  a  certain  development 
has  been  reached.  The  fact  that  certain  vertebrates  lose  all 
power  of  associative  memory  after  the  destruction  of  the  cere- 
bral hemispheres,  and  the  fact  that  vertebrates  in  which  the 
associative  memory  either  is  not  developed  at  all  or  only  slightly 
developed  (e.g.,  the  shark  or  frog)  do  not  differ,  or  differ  but 
slightly,  in  their  reactions  after  losing  the  cerebral  hemispheres, 
support  this  view.  The  fact  that  only  certain  animals  possess 
the  necessary  mechanical  arrangements  for  associative  memory, 
and  therefore  for  consciousness,  is  not  stranger  than  the  fact 
that  only  certain  animals  possess  the  mechanical  arrangements 
for  uniting  the  rays  from  a  luminous  point  in  one  point  on  the 
retina.     The  liquefaction  of  gases  is  an  example  of  a  sudden 

1  Loeb,  J.,  "Beitrage  ziir  Gehirnphysiologie  der  Wiiriner,"  Pflugers  Archiv, 
LVI,  247,  1894. 


Physiology  of  Central  Nervous  System        75 

change  of  condition  which  may  be  produced  when  one  variable 
is  changed;  it  is  not  surprising  that  there  should  be  sudden 
changes  in  the  ontogenetic  and  phylogenetic  development 
of  organisms  when  there  are  so  many  variables  subject  to 
change,  and  when  we  consider  that  colloids  easily  change  their 
state  of  matter. 

It  becomes  evident  that  the  unraveling  of  the  mechanism 
of  associative  memory  is  the  great  discovery  to  be  made  in  the 
field  of  brain  physiology  and  psychology.  But  at  the  same 
time  it  is  evident  that  this  mechanism  cannot  be  unraveled  by 
histological  methods,  or  by  operations  on  the  brain,  or  by 
measuring  reaction  times.  We  have  to  remember  that  all  life 
phenomena  are  ultimately  due  to  motions  or  changes  occurring 
in  colloidal  substances.  The  question  is,  Which  peculiarities 
of  the  colloidal  substances  can  make  the  phenomenon  of  asso- 
ciative memory  possible?  For  the  solution  of  this  problem 
the  experience  of  physical  chemistry  and  of  the  physiology  of 
the  protoplasm  must  be  combined.  From  the  same  sources 
we  must  expect  the  solution  of  the  other  fundamental  problems 
of  brain  physiology,  namely,  the  process  of  conduction  of 
stimuli. 


IV.    PATTERN  ADAPTATION  OF  FISHES   AND  THE 
MECHANISM  OF  VISION 


IV 

PATTERN  ADAPTATION  OF  FISHES  AND  THE  MECHAN- 
ISM OF  VISION! 

The  mechanism  of  the  action  of  the  brain  is  entirely 
miknown  to  us.  We  are  unable  to  look  into  the  active  brain 
and  the  objective  results  of  brain  action  are  in  general  so  differ- 
ent in  their  nature  from  the  external  stimulus  which  leads  to  the 
action  that  we  are  prevented  in  most  cases  from  drawing  any 
conclusions  concerning  the  nature  of  the  processes  occurring 
in  the  brain. 

From  results  obtained  in  experiments  on  dogs  Munk  stated 
years  ago  that  there  existed  a  projection  of  the  retina  on  a  part 
of  the  cortex  which  he  had  designated  as  the  visual  sphere  and 
that  the  extirpation  of  definite  parts  of  this  sphere  caused 
blindness  in  definite  parts  of  the  retina.  I  repeated  these 
experiments  but  was  not  able  to  confirm  his  statements. 
Henschen  has  recently,  however,  furnished  the  proof,  on  the 
basis  of  excellent  pathological  observations  on  man,  that  such 
a  projection  after  all  exists,  but  that  it  is  situated  in  another 
part  of  the  cortex  from  where  Munk  had  believed  it  to  be, 
namely,  in  the  area  striata.  Minkowski  was  able  to  confirm 
Henschen's  conclusions  through  experi  aents  on  dogs.  These 
observations  and  experiments  suggest  the  possibility  that  in 
vision  an  image  is  formed  not  only  on  the  retina  but  also  on  the 
cortex. 

The  possibility  that  vision  is  based  on  the  formation  of  an 
image  in  the  brain  is  supported  by  a  group  of  facts  which  to 
my  knowledge  have  never  received  any  consideration  in  this 
connection. 

1  Reprinted  from  Physiologisches  Centralblatt,  XXV,  No.  22,  1912.  This 
note  is  given  merely  as  a  suggestion  concerning  the  mechanism  underlying  certain 
brain  processes. 

79 


80  The   Mechanistic   Conception  of  Life 

It  has  been  known  for  some  time  that  many  animals, 
especially  certain  fishes,  adapt  their  color  and  pattern  to  the 
ground  upon  which  they  happen  to  be.  This  fact  has  been 
extensively  utilized  for  the  theory  of  natural  selection.  It 
seems  to  me  that  the  same  facts  furnish  also  the  proof  that  an 
image  of  the  objects  is  formed  in  the  brain.  Pouchet  many 
years  ago  showed  that  the  adaptation  of  fishes  to  the  ground 
ceases  as  soon  as  their  eyes  are  removed  or  as  soon  as  the  forma- 
tion of  retinal  images  is  prevented  through  the  turbidity  of  the 
refractive  media  of  the  eye.  This  fact  (confirmed  by  many 
observers)  proves  that  the  harmony  between  color  and  pattern 
of  the  skin  of  fishes  with  their  surroundings  is  transmitted 
through  the  retinal  image;  in  other  words,  that  the  so-called 
adaptation  of  fishes  to  their  surroundings  is  only  the  trans- 
mission of  the  retinal  image  to  the  skin. 

It  has,  moreover,  been  shown  that  the  destruction  of  the 
optic  fibers  and  the  optic  ganglia  in  the  brain  acts  like  the  extir- 
pation of  the  eyes;  and  finally  it  has  been  proved  that  the 
cutting  of  the  sympathetic  fibers  which  go  to  the  pigment  cells 
of  the  skin  also  prevents  the  formation  of  a  picture  of  the 
ground  on  the  skin.  Hence  we  know  the  path  by  which  the 
retinal  image  is  transferred  to  the  skin  of  fishes.  One  station 
is  the  ending  of  the  optic  fibers  in  the  brain.  Since  we  are  able 
to  prove  the  existence  of  an  image  of  the  object  on  the  retina 
of  fishes;  since  it  is  proved  that  the  image  on  the  skin  of  the 
fish  is  a  picture  of  the  retinal  image  but  not  of  the  object  (in 
this  case  the  ground)  itself;  since,  moreover,  the  transmission 
of  the  retinal  image  upon  the  skin  takes  place  through  the 
optic  nerve,  it  follows  that  the  image  must  pass  the  central 
stations  of  the  optic  nerve  during  the  transmission  to  the  skin. 

An  image  consists  of  a  number  of  points  of  different  intensity 
of  light,  the  mutual  arrangement  of  which  is  definite  and  char- 
acteristic for  the  object.  Sumner  has  shown  that  certain 
fishes  are  able  to  reproduce  on  their  skin  rather  complicated 


Pattern  Adaptation  of  Fishes  81 

patterns  (e.g.,  a  chess  board),  which  form  the  bottom  of  the 
aquarium.  This  reproduction  of  the  pattern  is  somewhat 
imperfect,  but  if  we  deduct  the  secondary  disturbing  factors  the 
fact  remains  that  the  pattern  on  the  skin  is  a  tolerably  true 
picture  of  the  pattern  of  the  ground.  There  exists,  therefore,  a 
definite  arrangement  of  the  images  of  the  different  luminous 
points  of  the  ground  on  the  retina  and  a  similar  arrangement  of 
the  images  of  the  luminous  points  on  the  skin  of  the  fishes.  We 
may  consider  each  point  of  the  retinal  image  as  a  luminous  or  a 
stimulating  point  which  produces  a  corresponding  image  point 
in  the  primary  optic  ganglia  through  the  action  of  the  nerve- 
fiber  through  which  it  is  connected  with  the  ganglia.  Every 
image  point  in  the  primary  optic  ganglia  may  be  considered 
again  as  a  luminous  or  stimulating  point  which  through  the 
mediation  of  a  special  nerve-fiber  influences  an  individual 
chromatophore  or  a  small  group  of  chromatophores  of  the  skin. 
Considering  the  fact  that  the  retina  is  a  mosaic,  we  cannot  well 
imagine  the  transmission  of  the  retinal  image  upon  the  skin 
in  any  other  way  than  by  assuming  that  the  relative  arrange- 
ment of  the  individual  points  of  the  retinal  image  is  preserved 
in  the  optic  fibers  and  the  end  ganglia  of  the  optic  nerve. 
Under  this  assumption  a  relative  distribution  of  the  stimulating 
intensities  must  occur  in  the  primary  optic  ganglion  which  cor- 
responds to  the  distribution  of  the  image  points  on  the  retina 
and  which  again  can  be  called  an  image. 

These  observations  in  fish  and  the  conclusions  drawn  in  this 
note  suggest  the  idea  that  vision  is  a  kind  of  telephotography. 


V.    ON  SOME  FACTS  AND  PRINCIPLES  OF 
PHYSIOLOGICAL  MORPHOLOGY 


V 

ON  SOME  FACTS  AND  PRINCIPLES  OF  PHYSIOLOGICAL 

MORPHOLOGY  1 

I.     HETEROMORPHOSIS^ 

The  various  organs  of  the  higher  animals  have  a  definite 
arrangement;  from  the  shoulders  arms  originate,  from  the  hips 
legs,  but  we  never  see  legs  growing  out  from  the  shoulders 
or  arms  from  the  hips.  In  the  lower  animals  the  same  definite 
arrangement  of  organs  exists. 

Fig.  22  gives  a  diagram  of  a  hydroid,  Antennularia  anten- 
nina,  which  is  quite  common  in  the  Bay  of  Naples.  From  a 
bundle  of  roots  or  stolons  a  straight  stem  arises  to  a  height  of 
six  inches  or  more.  From  this  main  stem  originate,  in  regular 
succession,  short  and  slender  branches,  which  carry  polyps  on 
their  upper  sides. 

In  this  animal  we  never  find  a  root  originating  at  the  apex, 
or  in  place  of  a  branch,  or  polyps  originating  on  the  under  side 
of  a  branch. 

In  observing  these  phenomena  the  question  arose :  What  are 
the  circumstances  which  determine  that  only  one  kind  of  organ 
shall  originate  at  certain  places  in  the  body?  It  occurred  to 
me  that  the  answer  to  this  question  might  be  obtained  by  finding 
out  first  of  all  whether  or  not  it  were  possible  to  make  any 
desired  organ  of  an  animal  grow  at  any  desired  place.  In  case 
this  could  be  done,  the  question  to  be  decided  was  whether  the 
same  circumstances  by  which  the  arrangement  of  organs  can 
be  changed  experimentally  also  determine  the  arrangement  of 

1  Reprinted  from  Biological  Lectures  delivered  at  the  Marine  Biological 
Laboratory  of  Woods  Hole,  1893,  by  courtesy  of  Ginn  &  Co, 

2  Untersuchungen  zur  physiologischen  Morphologie  der  Tiere.  I,  Hetero- 
morphosis,  Wtirzburg,  1891.  II,  Organbildung  und  Wachsthum,  Wtirzburg,  1892. 
Translated  in  Studies  in  General  Physiology. 

85 


86 


The  Mechanistic  Conception  of  Life 


\/ 


Fig.  23. — Diagram 
of  normal  regenera- 
tion if  a  piece  o  6  of 
Antennularia  is  hung 
up  vertically  in  the 
water.  The  piece 
forms  roots  W  at  the 
lower  end  h  and  a  new 
stem  S  at  the  upper 
end  a.  The  old  nor- 
mal arrangement  of 
organs  is  thus  restor- 
ed through  the  pro- 
cess of  regeneration. 


Fig.  24. — Diagram 
of  heteromorphic  re- 
generation in  Anten- 
nularia. A  piece  o  h 
cut  out  of  the  stem 
is  hung  up  in  an  in- 
verted position,  i.e., 
the  root  end  h  up- 
ward and  the  stem 
end  a  downward.  In 
this  case  the  apical 
end  a  forms  roots  W, 
and  the  basal  end  h 
forms  a  new  stem  S 
which  grows  upward. 


organs  in  the  natural  development.  The 
hydroid,  Antennularia  antennina,  above 
mentioned,  seemed  to  afford  a  suitable  sub- 
ject for  experimentation  in  an  attempt  to 
solve  this  problem  and  the  following  simple 
experiments  were  performed. 

A  piece  ah  (Fig.  23)  of  an  Antennu- 
laria  was  cut  out  and  hung  up  vertically  in 
the  water  of  the  aquarium,  the  apical  end 
a  above  and  the  root  end  h  below.  It  was  found  that  after  a 
few  days  the  root  end  h  had  formed  little  roots,  W,  which 


yJ- 


Fig.  22. — A  piece 
of  the  normal  stem 
of  Antennularia  an- 
tennina, a  hydroid  of 
the  Bay  of  Naples. 
Approximately  natu- 
ral size.  S  S,  stem. 
W,  stolons  or  roots. 


Physiological  Morphology 


87 


grew  downward,  and  the  apical  end,  a,  had  formed  a  new 
stem,  S. 

A  similar  piece  was  cut  out  from  another  specimen  and  was 
hung  upside  down  in  the  aquarium  (Fig.  24).  The  root  end  b, 
which  was  now  above,  formed  a  new  stem,  >S,  and  the  apical 
end  a,  which  was  below,  formed  roots,  W.  In  the  newly 
formed  stem  the  arrangement  of  the  organs  was  the  same  as 
in  the  normal  animal,  namely,  the  branches  which  were  growing 


Fig.  25. — From  nature.  Regeneration  of  a  piece  a  b  cut  out  from  the  stem 
of  Antennularia  and  put  horizontally  into  the  water.  The  branches  on  the  lower 
side  which  had  ceased  to  grow,  grow  downward  as  stolons  and  attach  themselves 
to  solid  bodies.     On  the  upper  side  a  new  stem  c  d  grows  vertically  upward. 

obliquely  upward  bore  polyps  on  their  upper  side.  From  this 
we  see  that  it  was  possible  to  substitute  a  root  for  a  stem  and 
an  apex  for  a  root.  This  phenomenon  of  the  substitution  of 
one  organ  for  another  I  termed  heteromorphosis.  If  the  excised 
piece  of  an  Antennularia  was  placed  horizontally  instead  of 
vertically  in  the  aquarium,  something  still  more  remarkable 
occured,  namely,  the  branches  on  the  lower  side  suddenly  began 
to  grow  vertically  downward,  and  these  downward  growing 
elements  were  no  longer  branches  but  roots  (Fig.  25).  This 
could  be  proved  by  their  physiological  reactions,  for  the  roots 
attach  themselves  to  the  surface  of  solid  bodies,  e.g.,  the  glass 


88 


The   Mechanistic  Conception  of  Life 


of  the  aquarium,  while  the  stems  never  show  such  a  reaction. 
These  new  parts  growing  out  from  the  branches  of  the  under 
side  of  the  stem  attached  themselves  to  the  solid  bodies  with 
which  they  came  in  contact.  Moreover,  they  were  positively 
geotropic  (that  is,  they  grew  toward  the  center  of  the  earth), 

while  the  branches  never 
showed  any  positive  geo- 
tropism.  The  branches 
on  the  upper  side  were 
not  transformed  into 
roots.  They  either  per- 
ished or  gave  rise  to  long, 
slender,  perfectly  straight 
stems,  which  grew  ver- 
tically upward.  These 
stems,  as  a  rule,  were  too 
slender  to  bear  branches, 
but  at  parts  of  the 
upper  surface  of  the 
main  stem  there  origi- 
nated new  stems  (c  d, 
Fig.  25),  which  grew 
vertically  upward  and 
produced  the  typical 
little  branches  bearing 
polyps. 

If  we  brought  the  stem  into  an  oblique  position  (Fig.  26), 
with  the  apex  a  upward,  from  every  element  of  the  main  stem 
new  stems  and  roots  originated,  but  with  this  difference,  that 
stems  always  originated  from  the  upper  side  of  an  element  and 
roots  from  its  lower  side.  If  the  stem  were  placed  in  an  oblique 
position,  with  the  root  end  above,  the  branches  on  the  under 
side  grew  out  as  roots,  and  at  the  upper  end  a  stem  arose  as 
usual. 


Fig.  26. — Diagrammatic  regeneration  in  a 
piece  a  6  of  a  stem  of  Antennularia  put  ob- 
liquely into  the  water.  On  the  upper  side  of 
the  stem  a  h  new  stems  S,  S„  S,„  grow  verti- 
cally upward,  while  at  the  lower  end  of  the 
piece  a  b  opposite  the  new  stems  roots  W, 
W„  W,„  grow  out. 

Tbis  influence  of  gravitation  is  found  only 
in  Antennularia  antennina,  not  in  other  forms 
of  Antennularia. 


Physiological  Morphology  89 

What  circumstances  had  all  these  experiments  in  common  ? 
The  stems  always  originated  from  the  upper  end  or  side  of  an 
element,  and  roots  always  from  the  lower  side  or  end  of  the  same 
element.  These  facts  can  be  explained  only  on  the  assump- 
tion that  in  this  case  gravitation  determines  the  place  of  origin 
of  organs. 

Now  we  may  ask  whether  the  action  of  this  force,  gravita- 
tion, is  also  responsible  for  the  natural  arrangement  of  the  organs 
in  this  form,  namely,  that  roots  appear  only  at  the  base  of  the 
stem  and  never  at  the  apex  or  in  the  place  of  a  branch.  I  believe 
that  this  is  the  case.  By  reason  of  its  negative  geotropism,  the 
stem  grows  vertically  upward.  Gravitation  does  not  permit 
roots  to  arise  at  any  place  except  at  the  under  side  of  the 
organs,  and  that  is,  under  normal  conditions,  at  the  base  of  the 
stem.  The  same  force  determines  that  polyps  can  originate 
only  on  the  upper  side  of  branches,  and  thus  the  general 
arrangement  of  organs  is  brought  about  by  gravitation.  But 
how  does  gravitation  determine  that  stems  grow  on  the  upper 
and  roots  at  the  under  side?  This  is  a  question  to  which  we 
shall  return  later. 

Fig.  27  gives  a  drawing  of  an  example  of  heteromorphosis 
in  Margelis,  sl  hydroid  common  at  Woods  Hole,  upon  which 
another  set  of  experiments  was  carried  on.  If  we  cut  off  a  stem, 
or  a  small  piece  of  a  stem  of  this  hydroid,  and  place  it  in  a  dish 
containing  sea-water,  protecting  it  carefully  from  every  motion, 
a  curious  change  takes  place  in  the  organism.  Almost  all,  and 
in  some  cases  all,  of  the  stems  which  touch  the  glass  give  rise 
to  roots  that  spread  out  and  very  soon  cover  a  large  area  of  the 
glass.  In  this  way  the  apical  end  of  a  stem  may  continue  to 
grow  as  a  totally  different  organ,  namely,  as  a  root.  Every 
organ  not  in  contact  with  some  solid  body  gives  rise  to  polyps. 
Even  the  main  root,  if  not  in  contact  with  a  solid  body,  no  longer 
grows  as  a  root,  but  gives  rise  to  a  great  number  of  small  polyps 
which  appear  at  the  end  of  long  stems.     Fig.  27,  which  Mr. 


90 


The  Mechanistic  Conception  of  Life 


Tower  was  kind  enough  to  draw  for  me,  shows  a  branch  which 
formed  roots  at  its  apex  and  polyps  at  its  roots  in  this  manner. 


Fig.  27. — Heteromorphosis  in  Margelis,  a  hydroid.     At  a  and  b,  where  the 
points  of  stems  touch  the  ground  of  the  aquarium,  new  roots  or  stolons  grow  out. 

The  stem  touched  the  bottom  of  the  dish  with  the  apical  ends, 
a  and  6.  All  these  ends  gave  rise  to  roots.  From  the  upper 
side  of  the  original  root,  which  was  not  in  contact  with  the 


b' 

Fig.  28. — Heteromorphosis  in  Pennaria.  A  piece  a  6  of  this  hydroid  was  cut 
out  and  put  into  a  jar  with  sea- water.  The  ends  a  and  b  touched  the  bottom  of  the 
jar.     At  both  points  new  roots  grew  out. 

glass,  later  on  small   polyps  grew  out.     Every  place  which 

was  in  contact  with  solid  bodies  gave  rise  to  roots,  and  every 

place  which  was  in  contact  with  sea-water  gave  rise  to  polyps. 

This  is  not  the  only  species  of  hydroid  found  at  Woods  Hole 


Physiological  Morphology  91 

in  which  such  forms  of  heteromorphosis  can  be  produced. 
Another  form,  Pennaria,  is  just  as  favorable.  In  Pennaria  I 
succeeded  repeatedly  in  producing  roots  at  both  ends  of  a 
small  stem  that  bore  no  polyps  (Fig.  28)  .^ 

In  these  experiments  on  Margelis  and  Pennaria  organs 
brought  into  contact  with  solid  bodies  continue  to  grow  as 
roots,  if  they  grow  at  all.  Organs  surrounded  on  all  sides  by 
water  continue  to  grow  in  the  form  of  polyps,  if  they  grow  at 
all.  In  Margelis,  contact  with  a  solid  body  plays  the  same  role 
as  did  gravitation  in  the  case  of  Antennularia.  In  what  way 
the  contact  may  have  an  influence  shall  be  mentioned  later  on, 
but  here  one  more  point  may  be  mentioned.  In  Antennularia, 
gravitation  not  only  determines  the  place  of  origin  of  the  various 
organs,  but  also  the  direction  of  their  growth;  the  stem, 
growing  upward,  is  negatively  geotropic,  the  root,  growing 
downward,  is  positively  geotropic.  In  Pennaria,  the  nature 
of  the  contact  not  only  determines  the  place  of  origin  of  the 
various  organs,  but  also  the  direction  of  their  growth.  If  we 
bring  an  outgrowing  polyp  of  Pennaria  into  contact  with  a 
solid  body,  the  polyp  begins  to  grow  away  from  the  body,  and 
the  new  stem  is  very  soon  nearly  perpendicular  to  the  part  of 
the  surface  with  which  it  came  into  contact. 

I  have  called  this  form  of  irritability  stereotropism.     We 

1  In  a  Tubularian  I  was  able  to  produce  the  opposite  result,  namely,  to  get 
an  animal  that  ended  at  both  ends  in  a  polyp  and  had  no  root.  Weismann  seems 
to  assume,  in  his  Germ  Plasm,  that  the  latter  result  is  to  be  explained  by  the 
principle  of  natural  selection,  inasmuch  as  an  animal  without  polyps  could  not 
continue  to  live,  and  hence  it  would  be  impossible  to  produce  roots  at  both  ends. 
In  Pennaria  this  supposed  impossibility  was  realized;  one  may  say  that  these 
roots  in  Pennaria  may  give  rise  later  on  to  polyps.  In  the  special  case  that  I 
observed  they  did  not,  although  as  a  rule  they  do;  but  the  same  is  the  case  in 
Tubularia,  in  which  polyps  also  arise  from  the  roots.  It  might  be  said,  perhaps, 
that  the  formation  of  roots  in  Pennaria  is,  for  some  reason,  absolutely  necessary; 
but  it  is  just  as  easy  to  produce  polyps  at  both  ends.  Even  if  it  were  possible  to 
reconcile  these  facts  with  the  principles  of  natural  selection,  causal  or  physiological 
morphology  would  not  gain  thereby,  as  the  circumstances  that  determine  the 
forms  of  animals  and  plants  are  only  the  different  forms  of  energy  in  the  sense  in 
which  this  word  is  used  by  the  physicist,  and  have  nothing  to  do  with  natxu*al 
selection. 


92  The  Mechanistic  Conception  of  Life 

may  speak  of  positive  stereotropism  in  the  case  of  the  root,  and 
of  negative  stereotropism  in  the  case  of  the  polyp. 

Here,  too,  we  may  ask  whether  the  contact  with  foreign 
bodies,  which  in  these  experiments  determines  the  arrangement 
of  the  various  organs,  may  not  have  the  same  effect  in  the 
natural  development  of  the  organism.  I  believe  that  such  is 
the  case.  Negative  stereotropism  forces  the  polyps  to  grow 
away  from  the  ground  into  the  water,  and  hence  parts  sur- 
rounded by  water  form  polyps  only.  Positive  stereotropism 
forces  roots  in  contact  with  the  ground  to  hold  to  it,  hence 
parts  in  contact  with  the  ground  give  rise  to  roots  only.  Thus 
it  happens  that,  under  ordinary  circumstances,  in  this  animal 
we  find  roots  only  at  the  base  where  it  touches  the  ground.  In 
other  hydroids  the  place  of  origin  of  the  different  organs  is 
determined  by  light,  and  in  others  we  find  more  complicated 
relations. 

It  may  appear  from  the  foregoing  that  such  cases  of  hetero- 
morphosis  are  confined  to  hydroids,  but  such  is  not  the  case. 
We  find  similar  cases  in  Tunicates.  Ciona  intestinalis,  a  solitary 
ascidian,  has  eye-spots  around  the  two  openings  into  the 
pharyngeal  cavity.  If  we  make  an  incision  eye-spots  are 
formed  on  both  sides  of  the  incision.^ 

II.    polarization 

While  the  foregoing  experiments  were  in  progress,  I  observed 
that  in  many  animals  I  was  unable  to  produce  any  kind  of 
heteromorphism.  These  animals  showed,  in  regard  to  the 
formation  of  organs,  a  phenomenon  with  which  we  are  familiar 
in  a  magnet.  If  a  magnet  is  broken  into  pieces,  every  piece 
has  its  north  pole  on  that  side  which  in  the  unbroken  magnet 
was  directed  toward  the  north.  Likewise,  there  are  animals 
every  piece  of  which  produces,  at  either  end,  that  organ  toward 

1  Since  this  was  written  phenomena  of  heteromorphosis  have  been  produced 
in  many  animals.  Herbst  found  that  in  crustaceans  an  antenna  could  be  caused 
to  be  formed  in  the  place  of  an  excised  eye,  Van  Duyne,  Bardeen,  and  Morgan 
observed  phenomena  of  heteromorphosis  in  Planarians  and  so  on  (1912). 


Physiological  Moephology 


93 


which  it  was  directed  in  the  normal  condition.     We  may  speak 

in  such  cases  of  polarization.     The  clearest  example  of  this  I 

found  in  an  actinian,  Cerianthus  memhranaceus. 
If  we  cut  a  rectangular  piece,  cd  ef,  out 

of  the  body-wall  of  Cerianthus  new  tentacles 

soon  begin  to  grow  out  of  this  piece,  but 

only  from  the  side  ef  (Fig.  29),  which  was 

directed  toward  the  oral  end  of  the  animal. 
Nothing  of  the  sort  oc- 
curs in  the  side  c  e,  or 
d  c  ,  or  f  d.  The  produc- 
tion of  tentacles  takes 
place  before  any  other 
regeneration  begins. 
The  same  polarization  is 
shown  in  the  following 
variation  of  the  preceding 
experiment.  If  we  make 
an  incision,  acb  (Fig.  30), 
into  the  body-wall  of  the  actinian,  only  the 
lower  lip,  b  c,  produces  tentacles,  while  the 
upper  lip,  a  c,  produces  none.  The  two 
ends  heal  together  in  such  a  way  that  one- 
half  of  a  mouth,  with  its  surrounding  ten- 
tacles, h  (Fig.  31),  is  formed.  It  is  curious 
to  see  how  these  tentacles  behave  if  we  offer 
them  bits  of  meat.  They  endeavor  to  force 
them  into  the  new  oral  disc,  where  the 
mouth  should  be,  and  only  after  a  struggle 

of  some  minutes  do  they  give  up  the  futile  attempt.     I  tried 

in  every  possible  way  to  produce  tentacles  in  the  aboral  end 

of  a  piece  which  had  been  cut  out,  but  without  success. 

Hydra  behaves,  as  regards  polarization,  a  little  differently 

from  Cerianthus.     If   we    make   an   incision   in   the   stem,   a 


■A 


Fig.  29. — Diagram- 
matic. If  a  piece  c  d 
ef  is  cut  out  from  the 
wall  of  Cerianthus,  a 
sea  anemone,  new- 
tentacles  are  formed 
only  at  the  upper  cut 
ef. 


Kj 


Fig.  30. — Diagram- 
matic. If  an  incision 
a  cb  is  made  into  the 
body  of  Cerianthus 
new  tentacles  grow 
out  only  from  the 
lower  edge  c  b. 


94 


The  Mechanistic  Conception  of  Life 


whole  new  oral  pole  grows  out,  but  otherwise  it  too  shows 
polarization. 

A  good  many  animals,  so  far  as  we  know,  reproduce  only 
the  lost  organ,  but  never  show  any  heteromorphism.     We  see, 


Fig.  31. — From  natiire.  Formation  of  a  second  head  in  Cerianthus  after  a 
lateral  incision  at  b.  Only  a  fraction  of  the  normal  nimiber  of  tentacles  are  formed 
corresponding  to  the  fraction  of  the  periphery  laid  bare  by  the  incision.  No  new 
mouth  is  formed,  but  if  a  piece  of  meat  is  offered  to  the  group  of  tentacles  at  b 
they  seize  it  and  press  it  to  the  place  where  a  mouth  ought  to  be,  showing  the 
purely  machine-like  character  of  all  these  reactions. 

therefore,  that  while  in  some  animals  we  are  able  to  produce 
heteromorphosis,  in  others  the  most  definite  polarization  exists, 
and  we  are  able  to  produce  regeneration  of  lost  parts  only  in  the 
arrangement  which  exists  in  the  normal  animal.  In  this  case 
we  must  assume  that  unknown  internal  conditions  determine 
the  arrangement  of  limbs. 

In  addition  to  examples  of  heteromorphosis  or  polarization 
occurring  separately,  we  find  cases  in  which  both  phenomena 


Physiological  Morphology 


95 


are  exhibited  by  the  same  animal.  If  we  cut  out  a  sufficiently 
large  piece  of  the  stem  of  Tuhularia  mesembryanthemum,  and 
place  it  in  the  bottom  of  a  dish  of  water, 
carefully  protected  from  jarring,  the  ante- 
rior end  of  the  piece  gives  rise  to  a  new 
polyp,  the  posterior  end  to  a  root;  but  if 
we  hang  up  the  stem  in  such  a  way  that  the 
posterior  end  does  not  touch  the  surface  of 
the  glass,  and  is  sufficiently  provided  with 
oxygen,  this  end,  too,  produces  a  polyp,  and 
we  have  a  true  case  of  heteromorphosis 
(Fig.  32) .  In  all  cases  the  polyp  at  the  oral 
end  is  formed  first,  and  a  relatively  long 
time  (one  or  more  weeks)  elapses  before 
the  aboral  polyp  is  formed.  Under  one  con- 
dition, however,  I  could  cause  the  stem  to 
form  a  polyp  at  the  aboral  as  quickly  as  at 
the  oral  end,  namely,  by  inhibiting  or  re- 
tarding the  formation  of  the  oral  poljrp. 
This  could  be  done  readily  by  diminishing 
the  supply  of  oxygen  at  the  oral  end.  In 
such  cases  the  aboral  polyps  were  produced 
almost  as  quickly  as  the  oral  polyps.^ 


III.      THE   MECHANICS   OF   GROWTH   IN 
ANIMALS 

In  order  to  arrive  at  an  explanation 
of  the  phenomena  of  organization  we  must 
ask  what  the  physical  forces  are  that 
determine  the  formation  of  a  new  organ. 
We  know  that  the  ultimate  sources  of 
energy  for  all  the  functions  of  living  bodies 


Fig.  32.  —  Hetero- 
morphosis in  Tuhula- 
ria. From  nature. 
The  normal  Tuhularia 
ends  at  one  end  in  a 
stolon,  at  the  other 
in  a  head  or  polyp. 
If  a  piece  o  6  is  cut 
out  and  suspended  in 
water  a  new  head  or 
polyp  c  and  d  is  formed 
at  both  ends.  We 
can  thus  produce  an 
animal  which  termi- 
nates in  a  head  at 
both  ends  of  its  body ; 
while  in  Fig.  28  an 
animal  was  represent- 
ed which  ended  at 
both  ends  in  a  stolon 
or  foot. 


1  It  was  found  later  independently  by  both  Godlewski  and  myseK  that  if  we 
ligature  the  stem  of  a  Tubularian  the  polyps  at  both  ends  are  formed  simultane- 
ously (1912). 


96  The   Mechanistic   Conception  of  Life 

are  chemical  processes.  The  question  is,  How  can  these 
chemical  forces  be  brought  into  relation  with  the  visible  changes 
which  take  place  in  the  formation  of  a  new  organ  ?  The  answer 
to  this  question  is  to  be  obtained  by  a  knowledge  of  the 
mechanics  of  growth.  It  is  very  remarkable  that  the  mechanics 
of  growth  forms  almost  an  empty  page  in  the  history  of  animal 
morphology  and  physiology.  I  can  refer  here  only  to  the  few 
experiments  I  have  made  on  this  subject;  but  fortunately  the 
subject  has  been  worked  out  very  carefully  in  plants,  and  as  my 
experiments  show  that  the  conditions  for  growth  in  animals 
are,  to  a  certain  extent  at  least,  the  same  as  the  conditions  for 
growth  in  plants,  we  have  the  beginning  of  a  basis  for  work. 

A  brief  outline  of  the  manner  of  growth  in  plants  is  as 
follows :  Before  the  cell  grows  it  forms  substances  which  attract 
water  from  the  surroundings,  or,  as  the  physicist  expresses  it, 
it  forms  substances  which  determine  a  higher  osmotic  pressure 
within  the  cell  than  did  the  substances  from  which  they  originate. 
The  walls  of  the  cell,  or  rather  the  protoplasmic  layer  that  lines 
the  cell -wall,  possesses  peculiar  osmotic  properties,  in  conse- 
quence of  which  it  allows  molecules  of  water  to  pass  through 
freely  while  remaining  resistant  to  the  passing  through  of  the 
molecules  of  many  salts  dissolved  in  the  water.  The  result  is 
that  when  substances  of  higher  osmotic  pressure  are  formed 
inside  the  cell,  water  from  the  outside  passes  in  until  the  pres- 
sure within  again  equals  the  pressure  without.  The  cell-wall 
becomes  stretched  and,  according  to  Traube,  new  material  is 
precipitated  in  the  enlarged  interstices,  thus  rendering  growth 
permanent.  This  method  of  growth  is  most  conspicuous, 
perhaps,  in  the  germinating  seed.  The  rising  temperature  in 
spring  produces  in  the  seed  substances  of  higher  osmotic  pres- 
sure (with  greater  attraction  for  water)  than  the  substances 
from  which  they  origuiate.  The  result  is  that  water  enters  the 
seed;  by  the  pressure  of  the  water  within  the  cells  their  walls 
are  stretched  out  and  the  seed  grows.     The   chemical  and 


Physiological  Morphology  97 

osmotic  changes  are  the  sources  for  the  energy  which  is  needed 
to  overcome  the  resistance  to  growth.^ 

In  order  to  ascertain  whether  I  could  determine  what  are 
the  mechanical  causes  of  growth  in  animals,  I  began  at  Naples 
some  experiments  on  Tuhularia  mesemhryanthemum.  I  chose 
long  stems  belonging  to  the  same  colony  and  distributed  them 
in  a  series  of  dishes  containing  sea-water  of  different  concentra- 
tions. In  some  of  the  dishes  the  concentration  had  been  raised 
by  adding  sodium  chloride,  and  in  others  it  had  been  lowered  by 
adding  distilled  water.  According  to  the  laws  of  osmosis  the 
amoimt  of  water  absorbed  by  the  cells  of  these  Tubularians 
differed  with  the  concentration  of  the  sea-water,  the  amount 
being  greatest  in  the  most  diluted  solution  and  least  in  the  most 
concentrated  solution.  If  now  in  reality  the  mechanics  of 
growth  is  the  same  for  animals  as  for  plants,  we  should  expect 
that  the  more  diluted  the  sea-water  the  more  rapid  would  be  the 
growth  in  the  Tubularian  stem.  Of  course,  finally,  a  limit  is 
reached  where  the  water  begins  to  have  a  poisonous  effect.  It 
was  found,  indeed,  that  within  certain  limits  of  concentration 
the  increase  in  the  length  of  the  stems  during  the  same  period 
was  greatest  in  the  most  diluted  and  least  in  the  most  concen- 
trated sea-water.  It  is  remarkable  that  the  maximum  of  growth 
took  place  not  in  sea-water  of  normal  concentration,  but  in 
more  diluted  sea-water,  though  this  of  course  may  not  be  the 
case  in  all  animals.  The  following  curve  (Fig.  33)  will  give  an 
idea  of  the  dependence  of  growth  upon  the  concentration  of 
the  sea-water  in  Tuhularia.  The  values  for  the  amount  of 
sodium  chloride,  in  100  cubic  centimeters  of  sea-water,  are 
represented  on  the  axis  of  the  abscissa,  the  values  for  the 
increase  in  growth  on  the  axis  of  ordinates. 

These  and  similar  experiments,  which  for  lack  of  space 
cannot  be  mentioned  here,  show  that  growth  in  animals  is 

1  The  substance  which  is  formed  and  which  causes  the  swelling  may  be  an 
acid.  I  found  that  acids  cause  a  swelling  of  muscles  and  it  has  since  been  shown 
that  this  is  a  general  phenomenon. 


98 


The   MECHAmsTic  Conception  of  Life 


determined  by  the  same  mechanical  forces  which  determine 
growth  in  plants.  An  obstacle  to  such  a  conclusion  seems  to  lie 
in  the  fact  that  many  plant-cells  have  solid  walls,  while  this  is 
not  the  case  in  most  animal  cells.  The  solid  cell-wall,  however, 
does  not  determine  the  peculiar  character  of  growth.  This 
character  is  determined  first,  by  chemical  processes  within  the 
cell,  which  result  in  a  higher  osmotic  pressure,  and,  secondly,  by 
the  osmotic  qualities  of  the  outer  layer  of  protoplasm,  which 


Fig.  33. — Curve  representing  the  influence  of  diluted  sea-water.  The 
abscissae  represent  the  concentrations,  the  ordinates  the  corresponding  growth 
in  the  unit  of  time.  The  maximum  growth  is  at  a  concentration  between  2  and  3 
per  cent  of  salt,  while  the  normal  concentration  is  indicated  by  the  vertical  line 
between  3  and  4. 


allows  water  to  pass  through  freely,  but  does  not  allow  all  salts 
dissolved  in  it  to  do  the  same.  Both  these  qualities  are  inde- 
pendent of  the  solid  cell-wall,  and  I  see  no  reason  why  the  animal 
cell  should  not  agree  in  these  two  salient  features  with  the 
plant-cell. 

In  order  that  the  foregoing  explanation  of  the  mec  hanism  of 
growth  in  the  animal  cell  might  be  based  only  upon  known  pro- 
cesses, it  was  necessary  to  find  out  whether,  in  case  of  growth, 
chemical  processes  of  such  a  character  take  place  that  substances 
of  higher  osmotic  pressure  are  formed  than  those  from  which 
they  originate.  Everyone  knows  that  by  exercise  our  muscles 
increase  in  size.     No  satisfactory  explanation  of  this  fact  has 


Physiological  Morphology  99 

been  given.  If  my  interpretation  of  the  method  of  growth 
were  correct,  I  must  expect  that  during  activity  substances  are 
formed  in  the  muscle,  which  determine  a  higher  osmotic  pressure 
than  those  from  which  they  originate.  This  is  exactly  the  case. 
Ranke  had  already  shown  that  the  blood  of  a  tetanized  frog 
loses  water  and  that  this  water  is  taken  up  by  the  muscles. 
In  experiments  which  were  carried  on  by  Miss  E.  Cooke  in  my 
laboratory,  we  were  able  to  show  directly  that  during  activity 
the  osmotic  pressure  inside  the  cell-wall  is  raised.  We  deter- 
mined the  concentration  of  a  solution  of  NaCl,  or  rather  of 
a  so-called  Ringer's  mixture,  in  which  the  gastroconemius  of  a 
frog  neither  lost  nor  took  up  water.  We  found  that  while 
this  concentration  for  the  resting  gastroconemius  was  about 
0.75  per  cent  to  0.85  per  cent,  for  the  gastroconemius  that 
had  been  tetanized  from  twenty  to  forty  minutes  it  varied  from 
1 . 2  per  cent  to  1 . 5  per  cent.^ 

This  increase  of  osmotic  pressure  inside  the  muscle-cell  leads, 
during  normal  activity,  to  a  taking  up  of  water  from  the  blood 
and  lymph,  and  the  consequence  is  an  increase  in  volume.  The 
same  muscle,  as  soon  as  it  ceases  to  be  active,  begins  to  decrease 
in  size.  Activity,  therefore,  plays  the  same  role  in  the  growth  of 
a  muscle  that  the  temperature  plays  in  the  growth  of  the  seed. 

I  tried  to  ascertain  whether  segmentation,  like  growth  in 
general,  is  influenced  by  the  amount  of  water  contained  in  the 
cell.  If  we  decrease  the  amount  of  water  in  the  egg  of  the 
sea-urchin  segmentation  is  retarded,  and  if  we  use  a  sufficiently 
high  concentration  of  sea-water  it  may  be  stopped  entirely. 
Therefore  the  amount  of  water  contained  in  the  cell  plays  still 
another  role  in  the  process  of  organization  and  influences  the 
process  of  cell-division. 

1  This  increase  in  osmotic  pressure  is  probably  caused  by  the  formation  of 
acid.  Two  years  after  the  publication  of  this  lecture  I  showed  that  the  muscle 
swells  in  an  isomotic  solution  if  this  solution  is  acid.  The  recent  work  of  Pauli 
and  Handovski  indicates  that  the  swelling  is  caused  through  a  formation  of  salt 
between  the  acid  and  a  weak  base,  e.g.,  a  protein.  The  protein  salt  is  more 
strongly  dissociated  than  the  protein  base  (1912). 


100  The   Mechanistic   Conception  of  Life 

iv.    the  artificial  production  of  double  and  multiple 
monstrosities  in  sea-urchins^ 

The  idea  that  the  formation  of  the  vertebrate  erabryo  is  a 
function  of  growth  has  been  made  the  basis  of  the  embryological 
investigations  of  His.  In  a  masterly  way,  His  has  shown  how 
inequality  of  growth  determines  the  differentiation  of  organs. 
In  the  blastoderm  of  a  chick,  for  example,  the  first  step  in  the 
formation  of  the  embryo  is  a  process  of  folding.  There  origi- 
nates a  head  fold,  a  tail  fold,  a  medullary  groove,  and  the  system 
of  amniotic  folds.  According  to  His,  all  these  processes  of 
folding  are  due  simply  to  inequalities  of  growth,  the  center  of 
the  blastoderm  growing  more  rapidly  than  the  periphery.  It 
can  be  shown,  very  simply,  that  such  a  process  of  unequal 
growth  must,  indeed,  lead  to  the  formation  of  exactly  such  a 
system  of  folds  as  we  find  in  the  blastoderm  of  a  chick.  If  we 
take  a  thin,  flat  plate  of  elastic  rubber,  and  lay  it  on  a  drawing- 
board,  we  can  imitate  the  stronger  growth  in  the  center  by 
sticking  two  tacks  into  the  middle  of  the  rubber,  a  short 
distance  apart,  and  then  pulling  them  in  opposite  directions. 
In  this  way  we  may  imitate  unequal  growth,  the  center  growing 
faster  than  the  periphery.  If  we  then  fix  the  tacks  in  the 
drawing-board,  so  that  the  rubber  in  the  middle  remains 
stretched,  we  get  the  same  system  of  folds  as  that  shown  by  the 
embryo  of  a  chick.  I  mention  this  way  of  demonstrating  the 
effects  of  unequal  growth  as  the  ideas  of  His  are  still  doubted 
by  some  morphologists. 

His  raised  the  question.  Why  is  growth  different  in  different 
parts  of  the  blastoderm?  But  instead  of  trying  to  answer  it 
from  the  physiological  standpoint  he  answered  it  from  the 
anatomical  standpoint.  According  to  him,  the  different  regions 
of  the  unsegmented  egg  correspond  already  to  the  different 
regions  of  the  differentiated  embryo.     But  this  so-called  theory 

1  Another  method  of  producing  twins  from  one  egg  is  discussed  in  the  last 
chapter  of  this  book. 


Physiological  Morphology  101 

of  preformed  germ-regions  gives  no  answer  to  the  question,  why 
some  parts  of  the  embryo  grow  faster  than  others.  Neverthe- 
less, it  is  not  necessarily  in  opposition  to  the  theory  of  growth 
offered  in  the  preceding  chapter.  Starting  with  the  idea  of  His, 
we  may  well  imagine  that  the  different  regions  of  the  ovum 
are  somewhat  different  chemically,  and  that  these  chemical 
differences  of  the  different  germ-regions  determine  the  differ- 
ences of  growth  in  the  blastoderm.  Thus  the  phenomena  of 
heteromorphosis  would  show  that,  in  some  animals  at  least,  the 
arrangement  of  preformed  germ-regions  may  be  changed  by 
gravitation,  light,  adhesion,  etc. 

It  must  be  asked,  however,  what,  from  the  standpoint  of 
causal  morphology,  determines  the  arrangement  of  the  different 
germ-regions  in  the  egg.  If  we  answer  "heredity,"  causal 
morphology  can  make  no  use  of  such  an  explanation.  Our 
blood  has  the  temperature  of  about  37°,  but  although  our 
parents  had  the  same  temperature,  the  heat  of  our  blood  is  not 
inherited,  but  is  the  result  of  certain  chemical  processes  in  our 
tissues.  Still  it  may  be  possible  that  the  molecular  forces  of 
the  chemically  different  substances  of  the  egg  determine  a 
separation  of  these  substances  and  thereby  give  rise  to  the 
chief  directions  of  the  future  embryo. 

Driesch  has  shown^  that  by  shaking  a  sea-urchin's  egg  in  the 
four-cell  stage  the  four  cells  may  be  separated,  and  each  one  be 
capable  of  giving  rise  to  a  complete  embryo,  which  differs  only 
in  size  from  the  normal  embryo.  If  the  theory  of  preformed 
germ-regions  with  its  later  modifications  were  true,  we  should 
expect  that  every  one  of  the  isolated  cells  would  give  rise  to 
one-fourth  of  an  embryo.  But  it  has  been  said  that  the  arti- 
ficial isolation  of  one  cleavage-cell  causes  a  process  of  post- 
generation or  regeneration.  Driesch,  moreover,  changed  the 
mode  of  the  first  cleavage  by  submitting  the  ovum  to  one-sided 
pressure.     In  this  way  the  nuclei  were  brought  into  somewhat 

1  Zeitschrift  f.  wissensch.  Zoologie,  LIII,  LV. 


102         The  Mechanistic  Conception  of  Life 

different  places  from  those  they  would  have  held  m  the  case  of 
normal  segmentation.  Still,  normal  embryos  resulted.  One 
might  object  again  that  the  preformation  of  the  germ-regions 
existed  in  the  protoplasm,  and  not  in  the  nucleus.  I  have  made 
a  series  of  experiments  to  the  results  of  which  these  objections 
cannot  be  made.  I  shall  describe  these  experiments  somewhat 
fully,  as  they  have  not  yet  been  published,  though  I  cannot 
enter  into  details  at  this  place. 

I  brought  eggs  of  a  sea-urchin,  within  ten  to  twenty  minutes 
after  impregnation,  into  sea-water  that  had  been  diluted  by  the 


Fig.  34  Fig.  35 

Fig.  34. — Fertilized  egg  of  a  sea-urchin  (Arbacia)  put  into  dilute  sea-water. 
The  protoplasm  swells  until  the  membrane  m  bursts  and  part  of  the  protoplasm 
b  flows  out ;  each  of  the  two  droplets  may  develop  into  a  blastula,  so  that  from 
such  an  egg  two  larvae  may  arise,  as  indicated  in  Fig.  35. 

addition  of  about  100  per  cent  distilled  water.  In  this  solution 
the  eggs  took  up  so  much  water  that  the  membrane  (m.  Fig.  34) 
burst  and  part  of  the  protoplasm  escaped  in  the  form  of  a  drop 
(b,  Fig.  34),  which  often,  however,  remained  in  connection 
with  the  protoplasm  inside  the  membrane  after  the  eggs  were 
brought  back  into  normal  sea-water.  These  eggs  gave  rise 
to  adherent  twins,  the  ejected  part  h  of  the  protoplasm,  as  well 
as  the  part  remaining  inside  the  membrane,  developing  into  a 
normal  and  perfectly  complete  embryo.  The  part  of  the  proto- 
plasm, which  at  first  had  connected  the  two  drops,  formed  the 
part  where  the  twins  remained  grown  together.  Of  course,  it 
often  happened  that,  by  accident  or  rapid  movement,  the  twins 
were  separated,  and  they  then  developed  into  perfectly  normal 
single  embryos.     Since  we  cannot  assume  that  in  every  case  the 


Physiological  Morphology  103 

same  part  of  the  protoplasm  escapes,  we  must  conclude  that 
every  part  of  the  protoplasm  may  give  rise  to  fully  developed 
embryos  without  regard  to  preformed  germ-regions.^  In  many 
eggs  a  repeated  outflow  of  the  protoplasm  takes  place.  In  such 
cases  each  of  the  drops  of  the  protoplasm  may  give  rise  to  an 
embryo,  and  I  obtained  not  only  double  embryos,  but  triplets 
and  quadruplets  all  grown  together. 

It  is  remarkable  that  the  development  of  these  monstrosities 
goes  on  nearly  at  the  same  rate  as  that  of  the  normal  embryo, 
provided  they  are  equally  well  supplied  with  oxygen  and  equally 
protected  from  microbes  and  infusoria.  The  development  in 
most  eggs  takes  place  in  so  regular  and  typical  a  manner  that  it 
seems  as  if  there  were  a  prearrangement  of  some  kind.  It  is, 
however,  perfectly  well  possible  that  this  prearrangement 
consists  in  a  separation  of  different  liquid  substances  in  the 
ovum  by  the  molecular  qualities  of  these  liquids.  Such  a 
separation,  of  course,  might  be  called  a  preformation  of  germ- 
regions,  but  it  would  be  something  totally  different  from  what 
is  now  understood  by  that  term. 

V.     THEORETICAL   REMARKS 

1.  All  life  phenomena  are  determined  by  chemical  processes. 
This  is  equally  the  case  whether  we  have  to  do  with  the  contrac- 
tion of  a  muscle,  with  the  process  of  secretion,  or  with  the  forma- 
tion of  an  embryo  or  a  single  organ.  One  of  the  steps  that 
physiological  morphology  has  to  take  is  to  show  in  every  case 
the  connecting  link  between  the  chemical  processes  and  the 
formation  of  organs.  I  have  tried  to  show  that  in  a  few  cases 
at  least  this  connecting  link  was  to  be  sought  in  the  changes  of 
osmotic  pressure  determined  by  the  chemical  changes  which 
take  place  in  the  growing  organ. 

But  this  fact  alone  does  not  explain  why  it  is  that  we  get 

1  In  the  light  of  more  recent  experiments  it  is  possible,  that  after  all  only  such 
pieces  can  develop  into  a  normal  embryo  which  contain  the  different  germ-regions 
(1912). 


104         The  Mechanistic  Conception  of  Life 

differences  in  the  forms  of  organs.  In  order  to  understand 
this  we  must  bear  in  mind  that  the  processes  of  growth  must 
necessarily  be  different  for  different  organs,  as  for  example  in 
the  formation  of  a  root,  and  the  formation  of  a  stem.  As 
growth  is  a  process  in  which  energy  is  used  up  in  overcoming 
the  resistance  to  growth,  differences  of  growth  can  only  be 
determined  either  by  differences  in  the  amount  of  energy  set  free 
in  the  growing  organ  or  by  differences  in  resistance.  Differ- 
ences in  the  energy  must  be  the  outcome  of  differences  in  the 
chemical  processes  which  determine  growth.  Therefore  we  are 
led  to  the  idea  that  differences  in  the  forms  of  different  organs 
must  be  determined  by  differences  in  their  chemical  constitu- 
tion, or,  if  the  chemical  constitutions  be  similar,  by  differences 
in  resistance  to  growth.  That  organs  which  differ  in  shape 
are  very  often  chemically  different  is  a  well-known  fact.  The 
formation  of  urea  in  the  liver  and  the  synthesis  of  hippuric 
acid  by  the  kidneys  are  the  consequences  of  chemical  differences. 

In  this  way  we  are  led  through  the  mechanics  of  growth  to  a 
conclusion  which  forms  the  nucleus  of  Sachs's  theory  of  organi- 
zation, namely,  ''that  differences  in  the  form  of  organs  are 
accompanied  by  differences  in  their  chemical  constitution,  and 
that  according  to  the  principles  of  science  we  have  to  derive  the 
former  from  the  latter."  According  to  Sachs  there  are  at  least 
as  many  ''spezifische  Bildungsstoffe "  in  a  plant  as  there  are 
different  organs.^ 

2.  In  adopting  the  theory  of  Sachs  and  applying  it  to  animal 
morphology,  we  must  avoid  a  mistake  very  often  made  even 
in  the  case  of  good  theories,  namely,  the  endeavor  to  explain 
special  cases  which  are  complicated  by  unknown  conditions. 
Huyghens  explained  by  his  theory  of  Kght  the  phenomena  of 
refraction,  but  he  could  not  and  did  not  attempt  to  explain  the 
sensations  of  color.     For  these  phenomena  the  wave  theory  of 

1  J.  Sachs,  Stoff  und  Form  der  Pflanzenorgajie,  Gesammelte  Abhandlungen, 
II,  1893. 


Physiological  Morphology  105 

light  remains  true,  but  color  sensations  depend  not  only  on  the 
wave  motion  of  the  ether,  but  also  on  the  chemical  and  physical 
structure  of  the  retina.  I  think  it  perfectly  safe  to  say  that 
every  animal  has  specific  germ  substances,  and  that  the  germ 
substances  of  different  animals  differ  chemically.  Its  chemical 
qualities  determine  that  from  a  chick's  egg  only  a  chick  can 
arise.  But  it  would  be  a  mistake  to  attempt  at  present  an 
explanation  of  how  the  unknown  chemical  nature  of  the  germ 
determines  all  the  different  organs  and  characters  that  belong 
to  the  species.  For  instance,  the  yolk  sac  of  the  Fundulus 
embryo  has  a  tiger-like  coloration.  We  might  say  that  these 
markings  may  be  due  to  a  certain  arrangement  of  molecules  or 
complexes  of  molecules  (determinants),  which  later  on  give  rise 
to  the  colored  places  of  the  yolk  sac,  but  I  foimd  that  this 
coloration  originates  in  a  manner  much  more  simple.  The 
pigment  cells  are  formed  irregularly  on  the  surface  of  the  yolk. 
The  pigment  is  chemically  closely  related  to  hemoglobin,  and 
so  its  formation  may  from  the  first  be  connected  with  the 
formation  of  the  blood  corpuscles.  But  the  arrangement  of 
the  pigment  cells  during  the  first  days  of  development  is  not 
such  as  to  produce  any  definite  markings.  They  lie  upon  the 
walls  of  the  blood-vessels  as  well  as  in  the  spaces  between  the 
capillaries  (Fig.  36).  Later  on,  however^  all  of  the  pigment 
cells  have  crept  upon  the  surface  of  the  neighboring  blood- 
vessels (Fig.  38).  I  succeeded  experimentally  in  showing  it  to 
be  probable  that  some  of  the  substances  contained  in  the  blood 
determine  this  reaction.  These  substances,  if  they  diffuse  from 
the  blood-vessel  and  touch  the  chromatophore,  make,  according 
to  the  laws  of  surface  tension,  the  protoplasm  of  the  chroma- 
tophore flow  toward  and  at  last  over  the  blood-vessel  and  form 
a  sheath  around  it,  while  the  gaps  between  the  blood-vessels 
become  empty  of  chromatophores.  In  this  way  the  chroma- 
tophores  are  arranged  in  stripes,  and  possibly  changes  in  the 
surface  tension,  and  not  a  preformed  arrangement  of  the  germ. 


106        The  Mechanistic  Conception  of  Life 


Fig.  36 


Fig.  37 


Fig.  38 


Figs.  36,  37,  and  38. — From  natiire.  The  origin  of  the  pattern  on  the  yolk 
sac  of  a  fish  embryo  {Fundulus  heterocUtus).  Fig.  36  is  a  drawing  of  the  blood- 
vessels at  the  surface  of  the  yolk  sac  at  an  early  stage  of  development.  The  black 
pigment  cells  show  no  definite  orientation  in  regard  to  the  blood-vessels.  Fig. 
37,  the  same  egg  a  few  days  later.  Here  we  notice  that  some  pigment  ceUs  show 
a  tendency  to  creep  on  the  blood-vessels.  Fig.  38,  the  same  egg  still  a  few  days 
later.  The  black  pigment  ceUs  have  completely  crept  on  the  blood-vessels  and 
formed  a  sheath  around  them.  The  red  chromatophores  are  omitted  in  this 
drawing. 

This  was  the  first  observation  proving  that  tropisms  play  a  role  in  the  arrange- 
ment of  the  organs  in  the  body. 


Physiological  Morphology  107 

determine  the  marking.  We  do  not  know  what  processes 
determine  the  coloration  of  animals  which  owe  their  markings 
to  interference  colors,  but  the  task  of  deriving  such  a  coloration 
in  the  adult  from  a  similar  arrangement  of  molecules  in  the 
germ  plasm  would  prove  too  much  even  for  a  genius  like 
Huyghens,  and  without  the  possibility  of  such  a  derivation  the 
theory  is  of  no  use. 

3.  The  reasons  why  roots  grow  on  the  under  side  of  the 
stem  of  Antennularia  and  stems  on  the  upper  side  can  only  be 
given  when  the  special  physical  and  chemical  conditions  inside 
the  stem  of  Antennularia  have  been  worked  out.  At  present  we 
can  only  think  of  possibilities.  It  is  possible  that  the  hypotheti- 
cal root  substances  of  Sachs  may  have  a  greater  specific  gravity 
than  the  substances  which  form  stems,  and  therefore  take  the 
lowest  position  in  the  cell.  Since  outgrowth  can  take  place 
only  at  the  free  surface  of  a  stem  or  branch,  roots  can  on  this 
assumption  grow  only  at  the  under  side  and  stems  only  at  the 
upper  side  of  an  element.  But  there  are  still  other  possibilities 
which  we  must  omit  here.  In  the  case  of  Margelis  and  other 
hydroids,  it  might  happen  that  contact  with  solid  bodies  pro- 
duced an  increase  of  surface  in  the  touched  elements  in  case  they 
contained  specific  root  substances,  while  the  opposite  took  place 
in  the  case  of  elements  containing  polyp  substances.  The  con- 
sequence would  be  an  increase  in  the  surface  of  the  roots  if  they 
came  into  contact  with  solid  bodies,  while  polyps  only  would 
grow  out  in  the  opposite  direction.  I  found,  indeed,  in  some 
forms  at  Naples  that  roots  of  hydroids  which  grew  free  in  the 
water  began  to  grow  much  faster  and  to  branch  off  more 
abundantly  when  brought  into  contact  with  solid  bodies.  But 
in  these  cases  we  must  wait  with  our  attempts  at  explanation 
until  the  physical  and  chemical  conditions  for  the  form  are 
worked  out.  For  the  same  reasons  I  will  not  go  into  a  discus- 
sion of  the  question  of  what  determines  the  polarization  of  ani- 
mals like  CerianthiLS.     It  may  suffice  to  suggest  the  possibility 


108         The  Mechanistic  Conception  of  Life 

that  in  polarized  animals  the  tissues  or  cells  may  have  such  a 
peculiar  structure  as  to  allow  the  specific  formative  substances 
to  migrate  or  arrange  themselves  only  in  one  direction,  while  in 
cases  of  heteromorphosis  migration  or  arrangement  in  every 
direction  or  in  several  directions  is  possible. 

4.  The  egg  of  a  sea-urchin  under  normal  conditions  gives 
rise  to  but  one  embryo.  This  circumstance  is  due  simply  to 
the  geometrical  shape  of  the  protoplasm,  which,  under  normal 
conditions,  is  that  of  a  sphere.  When  we  make  the  eggs  burst, 
the  protoplasm  outside  the  egg  membrane  and  that  which 
remains  within  it  assume  spherical  forms,  by  reason  of  the 
surface  tension  of  the  protoplasm.  When  this  happens,  as  a 
rule,  we  get  twins,  if  two  separate  segmentation  cavities  are 
formed,  and  only  one  embryo,  if  both  cavities  communicate 
with  one  another.  Whether  the  first  or  the  second  case  will 
happen  depends  upon  the  molecular  condition  of  the  part  of 
the  protoplasm  connecting  the  two  drops.  Therefore,  the 
number  of  embryos  which  come  from  one  egg  is  not  determined 
by  the  preformation  of  germ-regions  in  the  protoplasm,  or 
nucleus,  but  by  the  geometrical  shape  of  the  egg  and  the 
molecular  condition  of  the  protoplasm,  in  so  far  as  these  circum- 
stances determine  the  number  of  blastulae.  In  my  experiments, 
I  got  double  or  triple  embryos  when  the  egg  formed  two  or 
three  droplets  or  spheres,  as  every  sphere  gives  rise  to  a  blastula. 
In  Driesch's  experiments,  one  single  cell  of  the  four-cell  stage 
necessarily  formed  a  whole  embryo  after  it  had  been  isolated, 
as  it  assumed  the  shape  of  a  single  sphere  or  ellipsoid.  Of 
course,  there  must  be  a  limit  to  the  number  of  embryos  that  can 
arise  from  one  egg;  but  the  limit  is  not  due  to  any  preformation, 
but  to  other  circumstances,  the  chief  one  being  that  with  too 
small  an  amount  of  protoplasm  the  formation  of  a  blastula — 
from  merely  geometrical  reasons,  as  there  must  be  a  minimum 
size  for  the  cleavage-cells — becomes  impossible.^     Without  the 

1 1  stated  that  the  minimal  size  is  about  one-eighth  of  the  mass  of  the  sea- 
urchin's  egg  and  I  do  not  think  that  this  is  very  far  off  the  limit. 


Physiological  Morphology  109 

formation  of  the  blastula,  of  course  it  is  not  possible  to  get  the 
later  stages  which  are  determined  by  the  blastula. 

I  have  chosen  the  name  Physiological  Morphology  for  these 
investigations,  inasmuch  as  their  object  has  been  to  derive  the 
laws  of  organization  from  the  common  source  of  all  life  phenom- 
ena, i.e.,  the  chemical  activity  of  the  cell.  In  what  way  this 
is  to  be  done  is  indicated  in  the  chapter  on  the  mechanics  of 
growth. 

But  the  aim  of  Physiological  Morphology  is  not  solely 
analjrtical.  It  has  another  and  higher  aim,  which  is  synthetical 
or  constructive,  that  is,  to  form  new  combinations  from  the 
elements  of  living  nature,  just  as  the  physicist  and  chemist 
form  new  combinations  from  the  elements  of  non-living  nature. 


VI.    ON  THE  NATURE  OF  THE  PROCESS  OF 
FERTILIZATION 


ERRATUM 


P.  113,  line  13:   Dele  ^^not,"  so  as  to  read  as  follows:  ''The 
idea  that  spermatozoa  are  parasites  did  not  subside,"  etc. 


VI 

ON  THE  NATURE  OF  THE  PROCESS  OF  FERTILIZATION^ 

I 

Experimental  biology  is  a  very  recent  science.  Not  until 
recently  have  biologists  begiui  to  become  conscious  of  the 
uncertainty  of  conclusions  which  are  not  tested  and  verified  by 
adequate  experiments. 

Leeuwenhook  demonstrated  in  1677  the  existence  of  motile 
elements  in  the  sperm,  the  so-called  spermatozoa.  He  believed 
that  the  spermatozoa  represented  the  future  embryo.  The 
majority  of  his  contemporaries  assumed  that  the  spermatozoa 
were  parasitic  organisms  which  had  nothing  to  do  with  fertiliza- 
tion. The  idea  that  spermatozoa  are  s©t  parasites  did  not 
subside  until  it  was  proved  about  160  years  later  that  the 
spermatozoa  originate  from  the  cells  of  the  testes. 

That  sperm  was  needed  to  bring  about  fertilization  of  the 
egg  was  too  obvious  a  fact  to  escape  even  those  biologists  who 
never  made  an  experiment,  but  that  the  spermatozoa  and  not 
the  liquid  constituents  were  the  essential  element  in  the  sperm 
was  a  fact  which  could  not  be  established  except  experimentally. 
It  was  generally  assumed  that  no  direct  contact  between  sperm 
and  egg  was  necessary  and  that  something  volatile  contained 
in  the  sperm,  the  imaginary  "aura  seminalis"  was  sufficient 
for  the  act  of  fertilization.  That  contact  between  sperm  and 
egg  was  really  necessary  for  fertilization  was  at  last  proved 
experimentally  by  Jacobi  (1764)  who  showed  that  fish  eggs 
can  only  be  fertilized  if  the  sperm  is  brought  into  direct  con- 
tact with  the  eggs;  and  by  Spallanzani  who  put  the  males  of 
frogs  during  the  act  of  cohabitation  into  trousers  and  convinced 

1  Reprinted  from  Biological  Lectures  delivered  at  Woods  Hole,  1899,  by 
courtesy  of  Ginn  &  Co.,  Boston. 

113 


114         The  Mechanistic  Conception  of  Life 

himself  that  under  such  conditions  the  eggs  remained  unferti- 
lized although  the  ''aura  seminalis"  was  not  prevented  from 
acting  upon  the  eggs.  This  ended  the  reign  of  the  ''aura 
seminalis." 

It  was  reserved  to  two  experimenters,  Prevost  and  Dumas 
(the  latter  the  famous  chemist)  to  prove  that  the  spermatozoa 
are  the  essential  element  in  the  sperm.  They  made  the  simple 
experiment  of  filtering  the  sperm  and  demonstrated  that  the 
sperm  whose  spermatozoa  had  been  retained  by  the  filter  had 
lost  its  power  of  fertilizing  the  eggs.  But  even  this  did  not 
convince  many  of  the  descriptive  biologists  and  nine  years  later 
K.  E.  von  Baer  still  expressed  the  opinion  that  spermatozoa 
had  nothing  to  do  with  fertilization.  In  1843  the  entrance  of 
the  spermatozoon  into  the  egg  was  directly  observed  by  Barry 
and  this  fact  has  since  been  verified  by  an  endless  number  of 
investigators  for  the  egg  of  all  kinds  of  animals.  It  is  probably 
no  exaggeration  to  say  that  with  the  general  recognition  of  the 
experimental  method  in  biology  it  would  probably  have  taken 
about  as  many  years  as  it  took  centuries  to  establish  the  simple 
fact  that  the  spermatozoon  is  the  essential  element  in  sperm. 

The  mere  observation  of  the  fact  that  the  spermatozoon 
must  enter  the  egg  in  order  to  bring  about  fertilization  did  not 
lead  to  any  understanding  of  the  mechanism  of  the  activation  of 
the  egg.  Nevertheless  four  theories  or  rather  suggestions  were 
offered. 

The  first  theory  of  fertilization  is  a  morphological  one. 
According  to  this  theory,  it  is  the  morphological  structure  of  the 
spermatozoon  which  is  responsible  for  the  process  of  fertiliza- 
tion. 

The  second  theory  is  a  chemical  one.  According  to  this 
theory  it  is  not  a  definite  morphological  or  structural  element 
of  the  spermatozoon,  but  a  chemical  constituent,  that  causes 
the  development  of  the  egg.  Against  this  second  view  Miescher 
raised  the  objection  that  his  investigations  showed  the  same 


Nature  of  the  Process  of  Fertilization      115 

compounds  in  the  egg  and  the  spermatozoa.  I  do  not  believe 
that  this  objection  is  valid.  We  know  that  simple  variations 
in  the  configuration  of  a  molecule  have  an  enormous  effect  upon 
life  phenomena.  This  is  shown  among  others  by  the  work  of 
Emil  Fischer  on  the  relation  between  the  molecular  configura- 
tion of  sugars  and  their  fermentability.  When  Miescher  made 
his  experiments  he  was  not  familiar  with  such  possibilities. 
Moreover,  Miescher  was  not  able  to  state  whether  the 
spermatozoa  contain  enzymes  or  not. 

A  third  theory  was  a  physical  theory  (Bischof).  This 
theory  assumes  that  a  peculiar  condition  of  motion  exists  in 
the  spermatozoon  which  is  transmitted  to  the  egg  and  causes 
its  development.  It  should  be  said,  however,  that  this  idea 
is  not  so  very  different  from  the  chemical  conception,  because 
it  assumes  exactly  the  same  for  the  spermatozoon  that  Liebig 
assumes  for  the  enzymes.  Liebig  thought  that  the  enzymes 
owed  their  power  of  producing  fermentation  to  the  motions  of 
certain  atoms  or  groups  of  atoms. 

The  fourth  conception  is  the  stimulus  conception,  which 
was  originated  by  His.  According  to  this  conception  the  egg  is 
considered  as  a  definite  machine  which  if  once  wound  up  will 
do  its  work  in  a  certain  direction.  The  spermatozoon  is  the 
stimulus  which  causes  the  egg  to  undergo  its  development.  It 
is  to  be  said  in  connection  with  this  stimulus  conception  that 
the  main  point  at  issue  is  omitted  as  to  whether  the  stimulus 
carried  by  the  spermatozoon  is  of  a  physical  or  a  chemical 
character,  and  in  this  way,  of  course,  the  stimulus  conception  is 
nothing  but  a  disguised  repetition  of  the  chemical  or  physical 
theory  of  fertilization. 

All  these  theories  are  so  vague  that  we  do  not  need  to  be 
surprised  that  none  of  them  has  led  to  any  further  discovery. 
If  we  want  to  make  new  discoveries  in  biology,  we  must  start 
from  definite  facts  and  observations,  and  not  from  vague 
speculations.     Among  these  observations  the  most  important 


116         The  Mechanistic  Conception  of  Life 


are  those  on  parthenogenesis.  It  had  been  observed  for  a 
long  time  that  the  unfertiHzed  egg  of  the  silkworm  can  develop 
parthenogenetically.  It  was,  moreover,  known  that  plant  lice 
can  give  rise  to  new  generations  without  fertilization.  The 
most  impressive  fact  concerning  the  parthenogenesis  of  animals 
was  contributed  by  Dzierzon,  who  discovered  that  the  unferti- 
lized eggs  of  bees  develop  and  give  rise  to  males,  while  the 
fertihzed  eggs  give  rise  to  females.  Similar  conditions  seem  to 
exist  in  wasps.  It  is,  moreover,  certain  that  a  few  crustaceans 
show  parthenogenesis. 

A  beginning  of  parthenogenetic  development  had  been 
observed  in  the  case  of  a  great  many  marine  animals  which 
develop  outside  of  the  female  in  sea-water.  It  was  found  that 
such  eggs  when  left  long  enough  in  sea-water  may  divide  into 
two  or  three  cells,  but  no  farther.  On  the  other  hand,  in 
ovaries  of  mammals  now  and  then  eggs  were  found  that  were 
segmented  into  a  small  number  of  cells.^  These  facts  and  the 
occurrence  of  a  certain  class  of  tumors  in  the  ovary,  the  so-called 
teratomata,  suggest  the  possibility  of  at  least  partial  partheno- 
genesis in  the  eggs  of  mammals.  But  all  these  phenomena 
were  considered  to  be  of  a  pathological  character.  It  must  be, 
however,  admitted  that  we  cannot  utilize  these  facts  with  any 
degree  of  certainty  for  the  theory  of  fertilization,  as  in  this 
case  certainty  can  only  be  obtained  by  the  experiment.  It 
was  not  until  very  recently  that  such  experiments  were  made. 

II 

Eight  years  ago  I  observed  that  if  the  fertihzed  eggs  of  the 
sea-urchin  were  put  into  sea-water  whose  concentration  was 
raised  by  the  addition  of  some  neutral  salt  they  were  not  able 
to  segment,  but  that  the  same  eggs,  when  put  back  after  they 
had  been  in  such  sea-water  for  about  two  hours,  broke  up  into 
a  large  number  of  cells  at  once  instead  of  dividing  successively 

1  Hertwig,  O.,  Die  Zelle  und  die  Gewebe,  p.  239,  Jena,  1893. 


Nature  of  the  Process  of  Fertilization      117 

into  two,  four,  eight,  sixteen  cells,  etc.  Of  course  it  is  neces- 
sary for  this  experiment  that  the  right  increase  in  the  concen- 
tration of  the  sea-water  be  selected.  The  explanation  of  this 
fact  is  as  follows:  The  concentrated  sea-water  brings  about 
a  change  in  the  condition  of  the  nucleus  which  permits  a  division 
and  a  scattering  of  the  chromosomes  in  the  egg.^  As  soon  as 
the  egg  is  put  back  into  normal  sea-water  it  at  once  breaks  up 
into  as  many  cleavage-cells  as  nuclei  or  distinct  chromatin 
masses  had  been  preformed  in  the  egg.  Morgan  tried  the  same 
experiment  on  the  unfertilized  eggs  of  the  sea-urchin,  and 
found  that  the  unfertilized  egg,  if  treated  for  several  hours  with 
concentrated  sea-water,  was  able  to  show  the  beginning  of  a 
segmentation  when  put  back  into  normal  sea-water.  A  small 
number  of  eggs  divided  into  two  or  four  cells,  and,  in  a  few 
cases,  went  as  far  as  about  sixty  cells,  but  no  larvae  ever  devel- 
oped from  these  eggs.  Morgan^  had  used  the  same  concen- 
tration of  sea-water  as  Norman^  and  I  had  used  in  our  previous 
experiments.  I  had  added  about  2  grams  of  sodium  chloride 
to  100  c.c.  of  sea-water.  Norman  used  instead  of  this  3 J  grams 
of  MgCl2  to  100  c.c.  of  sea-water,  and  Morgan  used  the  same 
concentration.  Mead^  made  an  observation  somewhat  similar 
to  Morgan's  upon  Chaetopterus.  He  found  that  by  adding  a 
very  small  amount  of  KCl  to  sea-water  he  could  force  the  unfer- 
tilized eggs  of  Chaetopterus  to  throw  out  their  polar  bodies. 
The  substitution  of  a  little  NaCl  for  KCl  did  not  have  the 
same  effect.  While  continuing  my  studies  on  the  effects  of 
salts  upon  life  phenomena,  I  was  led  to  the  fact  that  the  peculiar 
actions  of  protoplasm  are  influenced  to  a  great  extent  by  the 
ions  contained  in  the  solutions  which  surround  the  cells.     As  is 

1  Loeb,  J.,  "Experiments  on  Cleavage,"  Journ.  of  Morph.,  VII,  1892. 

2  Morgan,  T.  H.,  "The  Action  of  Salt  Solutions,  etc.,"  Arch.  /.  Entwickelungs- 
mechanik,  VIII,  1899. 

3  Norman,  W.  W.,  "  Segmentation  of  the  Nucleus  without  Segmentation  of  the 
Protoplasm,"  Arch.  f.  Entwickelungsmechanik,  III,  1896. 

*  Mead,  A.,  "  The  Rate  of  Cell-Division  and  the  Fvmction  of  the  Centrosome," 
Woods  Hole  Biol.  Led.,  1898. 


118         The  Mechanistic   Conception  of  Life 

well  known,  if  we  have  a  salt  in  solution,  e.g.,  sodium  chloride, 
we  have  not  only  NaCl  molecules  in  solution,  but  a  certain 
number  of  NaCl  molecules  are  split  up  into  Na  ions  (Na  atoms 
charged  with  a  certain  quantity  of  positive  electricity)  and  CI 
ions  (CI  atoms  charged  with  the  same  amount  of  negative 
electricity) .  When  an  egg  is  in  sea-water,  the  various  ions  enter 
it  in  proportions  determined  by  their  osmotic  pressure  and  the 
permeability  of  the  protoplasm.  It  is  probable  that  some  of 
these  ions  are  able  to  combine  with  the  proteins  of  the  proto- 
plasm. At  any  rate,  the  physical  qualities  of  the  proteins  of 
the  protoplasm  (their  state  of  matter  and  power  of  binding 
water)  are  determined  by  the  relative  proportions  of  the 
various  ions  present  in  the  protoplasm  or  in  combination  with 
the  proteins.^  By  changing  the  relative  proportions  of  these 
ions  we  change  the  physiological  properties  of  the  protoplasm, 
and  thus  are  able  to  impart  properties  to  a  tissue  which  it  does 
not  possess  ordinarily.  I  have  found,  for  instance,  that  by 
changing  the  amount  of  sodium  and  calcium  ions  contained 
in  the  muscles  of  the  skeleton  we  can  make  them  contract 
rhythmically  like  the  heart.  It  is  only  necessary  to  increase 
the  number  of  sodium  ions  in  the  muscle  or  to  reduce  the  num- 
ber of  calcium  ions  or  do  both  simultaneously.^  On  the  basis 
of  this  and  similar  observations  I  thought  that  by  changing  the 
constitution  of  the  sea-water  it  might  be  possible  to  cause  the 
eggs  not  only  to  show  a  beginning  of  development  but  to 
develop  into  living  larvae,  which  were  in  every  way  similar 
to  those  produced  by  the  fertilized  egg. 

There  seemed  to  be  three  ways  in  which  this  might  be 
accomplished.  The  first  way  was  a  simple  change  in  the  con- 
stitution of  the  sea-water  without  increasing  its  osmotic  pres- 
sure.    The  second  way  was  to  increase  the  osmotic  pressure 

1  Loeb,  J.,  "On  lon-Proteid  Compounds  and  Their  Role  in  the  Mechanics  of 
Life-Phenomena,"  Amer.  Journ.  of  Phys.,  Ill,  1900. 

2  It  is  due  to  the  Ca  ions  of  our  blood  that  the  muscles  of  our  skeleton  do  not 
beat  rhythmically,  like  our  heart . 


Nature  of  the  Process  of  Fertilization      119 

of  the  sea-water  by  adding  a  certain  amount  of  a  certain  salt. 
The  third  way  was  by  combining  both  of  these  methods.  The 
first  way  did  not  lead  to  the  result  I  desired.^  All  the  various 
artificial  solutions  I  prepared  had  only  the  one  effect  of  causing 
the  unfertilized  egg  to  divide  into  a  few  cells,  but  I  was  not 
able  to  produce  a  blastula.  I  next  tried  the  effects  of  an 
increase  in  the  sea-water  by  adding  a  certain  amount  of  mag- 
nesium chloride.  In  this  case  I  had  no  better  results  than 
Morgan.  Very  few  eggs  began  to  divide,  but  these  did  not 
develop  beyond  the  first  stages  of  segmentation.  I  then  tried 
the  combination  of  both  methods.  The  osmotic  pressure  of 
ordinary  sea-water  is  roughly  estimated  to  be  the  same  as  that 
of  a  |n  NaCl  solution  or  a  -yn  MgClg  solution.  I  found,  after 
a  number  of  experiments,  that  by  putting  the  unfertilized  eggs 
of  the  sea-urchin  into  a  solution  of  60  c.c.  of  ^"-n  MgClg  solu- 
tion and  40  c.c.  of  sea-water  for  two  hours  the  eggs  began 
to  develop  when  put  back  into  normal  sea-water.  Such  eggs 
reached  the  blastula  stage.  I  do  not  think  that  anybody  has 
ever  seen  before  such  blastulae  as  resulted  from  these  imferti- 
lized  eggs.  As  these  eggs  had  no  membrane,  the  amoeboid 
motions  of  the  cleavage-cells  led  very  frequently  to  a  discon- 
nection of  the  various  parts  of  one  and  the  same  egg,  and  the 
outlines  of  the  egg  became  extremely  irregular.  The  blastulae 
showed,  as  a  rule,  the  same  outline  as  the  egg  had  in  the  morula 
stage.  It  was,  moreover,  a  rare  thing  that  the  whole  mass  of 
the  egg  developed  into  one  blastula.  The  disconnection  of  the 
various  cleavage-cells  led,  as  a  rule,  to  the  formation  of  more 
than  one  embryo  from  one  egg.  The  results  were  in  a  certain 
way  similar  to  those  I  had  obtained  when  I  caused  the  fertilized 
eggs  of  sea-urchins  to  burst.  In  such  cases  a  part  of  the  proto- 
plasm flowed  out  from  the  egg  but  was  able  to  develop.  These 
extraovates  had  no  membrane,  and  of  course  showed  some 
irregularity  in  their  outlines,  but  the  irregularity  in  this  case 

I  Later  experiments  gave,  however,  positive  results.     See  next  chapter. 


120         The  Mechanistic  Conception  of  Life 

was  far  less  than  that  observed  in  the  unfertilized  eggs  of  my 
recent  experiments.  But  although  I  had  thus  far  satisfied  my 
desire  to  see  the  unfertilized  eggs  of  the  sea-urchin  reach  the 
blastula  stage,  I  was  not  able  to  keep  these  eggs  alive  long 
enough  to  see  them  grow  into  the  pluteus  stage.  They  developed 
more  slowly  than  the  normal  eggs,  and  died,  as  a  rule,  on  the 
second  day. 

It  was  my  next  task  to  find  a  solution  which  would  allow 
the  eggs  to  reach  the  pluteus  stage.  I  found  that  this  can  be 
done  by  reducing  the  amount  of  magnesium  chloride  and 
increasing  the  amount  of  sea-water.  By  putting  the  unferti- 
lized eggs  for  about  two  hours  into  a  mixture  of  equal  parts  of 
-?^-n  MgCla  and  sea-water,  the  eggs,  after  they  were  put  back 
into  normal  sea-water,  not  only  reached  the  blastula  stage,  but 
went  into  the  gastrula  and  pluteus  stages.  The  bJastulae  that 
originated  from  these  eggs  looked  much  healthier  and  more 
normal  than  those  of  the  former  solution  with  more  MgCl2. 
Of  course  as  these  unfertilized  eggs  had  no  membrane  it 
happened  but  rarely  that  the  whole  mass  of  an  egg  developed 
into  one  single  embryo.  Quadruplets,  triplets,  and  twins  were 
much  more  frequently  produced  than  a  single  embryo.  The 
outlines  of  each  blastula  were  much  more  spherical  than  in  the 
previous  experiment.  These  eggs  reached  the  pluteus  stage  on 
the  second  day  (considerably  later  than  the  fertilized  eggs  do). 
Thus  I  had  succeeded  in  raising  the  unfertilized  eggs  of  sea- 
urchins  to  the  same  stage  to  which  the  fertilized  eggs  can  be 
raised  in  the  aquarium.  I  have  not  yet  succeeded  in  raising  the 
fertilized  eggs  in  my  laboratory  dishes  beyond  the  pluteus  stage. 

Though  I  do  not  wish  to  go  into  the  technicalities  of  these 
experiments,  I  must  mention  a  few  of  the  precautions  that  I 
took  in  order  to  guard  against  the  possible  presence  of  sperma- 
tozoa in  the  sea-water.^     The  reader  who  is  interested  in  this 

1  Today  it  may  seem  strange  that  I  had  to  m^eet  such  objections,  but  when  my 
first  papers  on  artificial  parthenogenesis  appeared,  very  few  biologists  were  willing 
to  accept  the  correctness  of  my  statements.  The  most  absurd  sources  of  error 
were  suggested. 


Nature  of  the  Process  of  Fertilization      121 

technical  side  of  the  experiments  will  find  all  the  necessary  data 
in  my  publication  in  the  American  Journal  of  Physiology.^ 
Here  I  wish  only  to  mention  the  following  points: 

1.  These  experiments  were  made  after  the  spawning  season 
was  practically  over. 

2.  Bacteriological  precautions  were  taken  against  the  possi- 
bility of  contamination  of  the  hands,  dishes,  or  instruments 
with  spermatozoa. 

3.  The  spermatozoa  contained  in  the  sea-water  lose,  accord- 
ing to  the  investigation  of  Gemmill,^  their  fertilizing  power 
within  five  hours  if  distributed  in  large  quantities  of  sea-water. 

4.  We  have  a  criterion  by  which  we  can  tell  whether  the 
egg  is  fertilized  or  not  in  the  production  of  a  membrane.  The 
fertilized  egg  forms  a  membrane  and  the  unfertilized  egg  has  no 
distinct  membrane.  None  of  the  unfertilized  eggs  that  devel- 
oped artificially  had  a  membrane.^ 

5.  With  each  experiment  a  number  of  control  experiments 
were  made.  Part  of  the  unfertilized  eggs  were  put  into  the 
same  normal  sea-water  that  was  used  for  the  eggs  that  did 
develop.  None  of  these  eggs  that  remained  in  normal  sea- water 
formed  a  membrane  or  showed  any  development,  except  that  a 
few  of  them  were  divided  into  two  cells  after  about  twenty- 
four  hours. 

6.  I  made  another  set  of  control  experiments  by  putting  a 
lot  of  eggs  of  the  same  female  into  a  solution  which  differed  less 
from  the  normal  sea-water  than  the  one  which  caused  the 
formation  of  blastulae  or  plutei  from  the  unfertilized  eggs. 

1  Loeb,  J.,  "  On  the  ArtiflciaL Production  of  Normal  Larvae  from  the  Unferti- 
lized Egg  of  the  Sea-Urchin,"  Amer.  Journ.  of  Phys.,  III. 

2  Gemmill,  "The  Vitality  of  the  Ova  and  Spermatozoa  of  Certain  Animals," 

Journ.  of  Anat.  and  Phys.,  1900. 

3  The  method  used  in  these  experiments  was  primitive  inasmuch  as  no  ferti- 
lization membrane  was  formed.  A  few  years  later  I  found  a  method  for  the 
artificial  production  of  a  fertilization  membrane,  which  is  described  in  the  next 
paper.  In  the  earlier  experiments  in  which  no  fertilization  membrane  was 
developed,  nevertheless  a  change  in  the  cortical  layer  of  the  egg  was  brought 
about  by  the  combined  action  of  the  hydroxyl-ions  of  the  solution,  and  the 
increased  osmotic  pressure. 


122         The   Mechanistic  Conception  of  Life 

In  this  case  it  was  shown,  that  although  these  eggs  received  the 
same  sea-water  as  the  ones  which  developed,  and  although 
they  were  injured  less  than  the  ones  which  developed,  yet  not 
one  single  egg  formed  a  membrane  or  reached  the  blastula 
stage.  If  the  sea-water  had  contained  any  spermatozoa  these 
eggs  should  have  reached  the  blastula  stage.^  Hence,  as  in 
nine  different  series  of  experiments  these  results  were  confirmed, 
we  may  assume  that  by  treating  the  eggs  for  two  hours  with  a 
solution  of  equal  parts  of  a  %^n  MgClg  solution  and  sea-water 
we  can  cause  them  to  develop  parthenogenetically  into  plutei. 

Ill 

What  conclusions  may  we  draw  from  these  results  ?  If  we 
wish  to  avoid  wild  and  sterile  speculations,  I  think  we  should 
confine  ourselves  to  the  following  question:  What  alterations 
can  be  produced  in  an  egg  by  treating  it  for  two  hours 
with  a  solution  of  equal  parts  of  \^-n  MgClg  and  of  sea-water  ? 
Even  in  this  regard  we  can  only  give  a  very  indefinite  answer 
which,  however,  will  have  to  be  in  the  following  direction :  The 
bulk  of  our  protoplasm  consists  of  colloidal  substances.  This 
material  easily  changes  its  state  of  matter  and  its  power  of 
binding  water.  It  seems  probable  that  changes  of  these  two 
qualities  are  mainly  responsible  for  muscular  contraction  and 
perhaps  amoeboid  motions.  Among  the  agencies  that  cause 
changes  of  these  physical  qualities  we  know  of  three  that  are 
especially  powerful.  The  one  is  specific  enzymes  (trypsine, 
plasmase,  etc.).  The  second  is  ions  in  definite  concentration. 
The  concentration  varies  for  various  ions.  The  third  agency 
is  temperature.  In  our  experiments  it  is  obvious  that  only  the 
second  possibility  can  have  been  active.  I  do  not  consider 
it  advisable  to  enter  into  theoretical  discussions  beyond  these 

1  Through  other  control  experiments  I  convinced  myself  that  a  treatment  of 
eggs  or  spermatozoa  with  equal  parts  of  a  -g"n  MgClg  solution  and  sea-water 
diminishes  the  impregnability  of  the  eggs  and  annihilates  the  fertilizing  power  of 
spermatozoa  in  a  very  short  time. 


Nature  of  the  Process  of  Fertilization      123 

statements.  The  next  question  that  should  be  raised  would  be 
whether  the  spermatozoa  act  in  the  same  way.  It  is  true  that 
the  spermatozoon  contains  a  considerable  proportion  of  salts, 
especially  KgPO^,  but  it  may  contain  enzymes  or  it  may  con- 
tain substances  which  have  similar  effects  upon  the  physical 
qualities  of  the  colloids,  like  the  three  agencies  mentioned  above. 
In  the  last  volume  of  these  lectures  I  pointed  out  that  it  is 
impossible  to  derive  all  the  various  elements  that  constitute 
heredity  from  one  and  the  same  condition  of  the  egg.^  Our 
recent  experiments  suggest  the  possibility  that  different  con- 
stituents of  the  egg  are  responsible  for  the  process  of  fertiliza- 
tion and  for  the  transmission  of  the  hereditary  qualities  of  the 
male.  While  we  are  able  to  produce  the  process  of  fertilization 
by  a  treatment  of  the  imfertilized  egg  with  certain  salts  in 
certain  concentrations,  we  cannot  hope  to  bring  about  the 
transmission  of  the  hereditary  qualities  of  the  male  by  any  such 
treatment.  Hence,  the  inference  must  be  that  the  transmis- 
sion of  the  hereditary  qualities  of  the  male  and  the  agency  that 
causes  the  process  of  fertilization  are  not  necessarily  one  and 
the  same  thing.  I  consider  the  chief  value  of  the  experiments 
on  artificial  parthenogenesis  to  be  the  fact  that  they  transfer 
the  problem  of  fertilization  from  the  realm  of  morphology 
into  the  realm  of  physical  chemistry .^ 

1  Loeb,  J.,  "  The  Heredity  of  the  Marking  in  Fish  Embryos,"  Woods  Hole  Biol. 
LecL,  Boston,  1899. 

2  This  paper  was  written  immediately  after  I  had  succeeded  in  producing 
larvae  from  the  unfertilized  egg.  In  the  following  years  the  methods  of  artificial 
parthenogenesis  were  improved  and  this  led  to  the  xinraveling  of  the  mechanism 
by  which  the  spermatozoon  causes  the  egg  to  develop.  An  account  of  this  work 
is  given  in  the  two  following  papers. 


VII.    ON  THE  NATURE  OF  FORMATIVE  STIMU- 
LATION (ARTIFICIAL  PARTHENOGENESIS) 


VII 

ON  THE  NATURE  OF  FORMATIVE  STIMULATION 
(ARTIFICIAL  PARTHENOGENESIS)! 

PREFACE 

The  title  of  this  paper  was  chosen  in  reference  to  Virchow's 
paper  on  ''Stimulation  and  Irritability"  (Virchow's  ArchiVf 
XIV,  1,  1858)  in  which  he  discriminates  between  three  forms  of 
stimulation :  functional,  nutritive,  and  formative.  By  formative 
stimuli  he  means  those  which  give  rise  to  nuclear  and  cellular 
division.  He  considers  as  the  classic  example  for  formative 
stimulation  the  fertilization  of  the  egg  and  the  parallel  drawn 
by  him  between  this  process  and  the  causation  of  a  pathological 
process  of  growth  is  so  characteristic  that  we  may  quote  it  in  full : 

If  we  admit  the  identity  between  the  pathological  and  the  embry- 
onic neoformation,  the  egg  will  have  to  be  considered  as  the  analogue 
of  the  pathological  mother  cell  and  the  act  of  impregnation  as  the 
analogue  of  pathological  stimulation.  This  view  is  not  essentially 
altered  through  the  discovery  of  the  entrance  of  the  spermatozoon 
into  the  egg,  since  there  is  no  reason  to  consider  the  spermatozoon  as 
the  direct  morphological  starting-point  for  the  development  of  definite 
parts  of  the  egg.  If,  as  seems  to  be  the  case,  the  spermatozoa  are 
dissolved  in  the  egg,  they  carry  into  it  only  certain  chemical  substances, 
which  serve  as  specific  stimuli,  by  calling  forth  new  chemical  and 
morphological  arrangements  of  the  atoms.  Each  specific  contagium 
offers  the  same  possibilities. 

The  supposition  prevalent  at  Virchow's  time,  that  the 
spermatozoon  is  entirely  dissolved  in  the  egg  was  not  correct; 
but  his  view,  that  the  spermatozoon  carries  chemical  substances 
into  the  egg,  which  form  the  stimulus  for  its  development,  is 
perfectly  correct;  and  likewise  the  analogy  between  the  causa- 
tion of  the  development  of  the  egg  by  a  spermatozoon  and  the 
causation  of  a  pathological  growth  seems  correct.     I  therefore 

1  Address  delivered  at  the  International  Medical  Congress  at  Budapest,  1909. 

127 


128         The   Mechanistic  Conception  of  Life 

believe  that  it  may  be  of  interest  to  the  medical  profession 
to  follow  me  in  a  brief  survey  of  my  experiments  on  artificial 
parthenogenesis  and  the  causation  of  the  development  of  the 
egg  by  a  spermatozoon. 

I 

Cellular  physiology  has  shown  that  tissues  and  organs 
develop  only  from  cells  through  nuclear  and  cellular  division. 
The  conditions  which  cause  cells  to  divide  and  to  develop  into 
new  normal  or  pathological  tissues  have,  since  Virchow,  been 
called  formative  stimuli.  It  is  the  task  of  modern  biology  to 
ascertain  first  what  is  the  nature  of  these  stimuli,  and  second, 
which  change  occurs  in  the  cell  in  the  process  of  formative 
stimulation.  Virchow  already  emphasized  the  fact  that  the 
fertilization  of  the  egg  is  the  model  of  all  phenomena  of  forma- 
tive stimulation  and  that  the  spermatozoon  may  be  considered 
as  the  formative  stimulus  in  this  case. 

Pathologists  have  not  yet  succeeded  in  determining  what 
the  physico-chemical  nature  of  the  formative  stimulus  in  the 
case  of  a  tumor  is,  or  what  changes  a  cell  undergoes  in  such  a 
process.  This  task  has,  however,  been  accomplished  to  a  high 
degree  in  the  animal  egg,  and  it  may  therefore  interest  the 
pathologist  and  the  physician  in  general  to  become  familiar 
with  the  essential  features  of  the  data  thus  obtained. 

It  is  known  that  aside  from  a  few  exceptions  the  animal  egg 
can  only  develop  if  a  spermatozoon  enters  into  it.  If  no  sperma- 
tozoon enters,  as  a  rule  no  segmentation  of  the  egg  takes  place 
and  it  perishes  after  a  comparatively  short  period  of  time.  The 
questions  which  I  tried  to  solve  were  the  following:  By  which 
physico-chemical  agencies  does  the  spermatozoon  cause  the 
egg  to  divide  and  to  develop  into  an  embryo;  and  second,  which 
changes  does  the  egg  undergo  in  this  formative  stimulation  by 
a  spermatozoon  ?  Or  in  other  words,  what  is  the  mechanism  by 
which  the  unfertilized  egg  is  caused  to  segment  and  to  develop  ? 


Nature  of  Formative  Stimulation  129 

Two  ways  were  open  to  find  an  answer  to  this  question: 
first  to  try  to  cause  the  development  of  the  unfertiUzed  egg 
with  extracts  from  sperm.  I  have  spent  a  good  deal  of  time  in 
trying  to  succeed  in  this  task,  but  met  at  first  with  only  negative 
results  for  the  reason  that  I  used  at  first  only  extracts  from  the 
sperm  of  the  same  species  of  animals  from  which  the  eggs  were 
taken.  Only  recently  have  I  found  that  the  extract  of  sperm  is 
effective  only  if  it  is  taken  from  a  foreign  species.  We  shall 
return  to  this  curious  fact  later  on  and  show  that  it  has  a 
bearing  upon  the  problem  of  the  immunity  of  our  cells  to  the 
lysins  of  our  body. 

The  second  way  which  could  lead  to  a  decision  of  the  ques- 
tion concerning  the  nature  of  formative  stimulation  lay  in  the 
direction  of  artificial  parthenogenesis,  i.e.,  of  the  causation  of 
the  development  of  the  animal  egg,  not  by  extracts  of  sperm 
but  directly  by  physico-chemical  agencies.  This  method  of 
procedure  has  a  special  advantage.  Since  in  this  case  we  know 
the  nature  of  the  agencies  we  employ,  it  is  easier  to  get  an 
insight  into  the  mechanism  by  which  they  cause  the  development 
of  the  egg;  while  if  we  work  with  extracts  of  sperm  we  are  in 
the  dark  as  to  the  chemical  character  of  the  active  substances. 

II 

We  will  begin  with  a  description  of  the  method  of  artificial 
parthenogenesis  in  the  egg  of  the  Californian  sea-urchin, 
since  here  this  method  has  been  worked  out  most  completely. 
It  may  be  mentioned  that  in  the  eggs  of  many  animals  the  effect 
of  the  entrance  of  the  spermatozoon  manifests  itself  almost 
instantly  by  a  characteristic  change,  namely,  the  formation 
of  the  so-called  membrane  of  fertilization.  Briefly  stated  this 
process  may  possibly  consist  in  the  entrance  of  sea-water 
between  the  surface  film  and  the  protoplasm  of  the  egg,  where- 
by the  former  is  lifted  up  from  the  protoplasm  of  the  egg  and 
separated  from  it  by  a  more  or  less  wide,  clear  space.     Figs.  1 


?■> 


130         The   Mechanistic  Conception  of  Life 

and  2  (page  7)  show  these  changes  in  the  sea-urchin  egg.  Fig. 
1  represents  the  unfertilized  egg,  Fig.  2  shows  the  same  egg 
after  the  entrance  of  the  spermatozoon. 

In  1905  I  succeeded  in  finding  a  method  by  which  it  is 
possible  to  call  forth  the  formation  of  a  membrane  of  fertiliza- 
tion without  apparent  injury  to  the  egg.  This  method  consists 
in  putting  the  eggs  for  about  two  minutes  (at  a  temperature 
of  15°)  into  a  mixture  of  50  c.c.  of  sea-water +3  c.c.  of  an  n/10 
lower  monobasic  fatty  acid,  e.g.,  acetic,  propionic,  butyric,  or 
valerianic  acid.  In  this  mixture  no  membrane  formation 
takes  place;  if,  however,  the  eggs  are  transferred  into  normal 
sea-water  all  the  eggs  form  a  perfect  fertilization  membrane. 
The  experiments  showed  that  this  process  of  membrane  forma- 
tion is  the  essential  condition  which  causes  the  egg  to  develop. 
In  all  these  eggs  in  the  course  of  the  next  hours  after  the  mem- 
brane formation  those  changes  begin  which  lead  to  a  cell- 
division.  If  the  temperature  is  very  low  not  only  cell-divisions 
begin  but  the  egg  may  develop  into  a  swimming  larva;  it 
reaches  the  so-called  blastula  stage.  At  room  temperature, 
however,  the  artificial  production  of  a  membrane  in  the  egg 
by  fatty  acid  only  calls  forth  a  nuclear  and  possibly  a  cell- 
division;   after  this  the  egg  slowly  begins  to  disintegrate. 

We  therefore  see  that  the  artificial  membrane  formation 
by  a  fatty  acid  induces  the  developmental  process,  but  that 
at  ordinary  temperature  the  latter  does  not  go  far.  In  order 
to  cause  a  complete  development,  a  second  influence  is  needed, 
as  we  shall  see  later. 

Before  we  describe  this  second  influence,  another  question 
has  to  be  settled,  namely,  how  we  know  that  the  membrane 
formation  and  not  any  other  action  of  the  acid,  e.g.,  a  catalytic, 
is  the  formative  stimulus  in  this  case.  The  answer  is,  that  if 
we  apply  the  acid  but  prevent  the  changes  leading  to  a  mem- 
brane formation,  divisions  of  the  nucleus  and  of  the  cell  do  not 
occur.     On  the  other  hand,  we  shall  see  later  on  that  we  can 


Nature  of  Formative  Stimulation  131 

call  forth  the  membrane  formation  not  alone  by  fatty  acids 
but  by  a  number  of  different  agencies  and  that  all  these  means 
act  as  formative  stimuli. 

The  causation  of  the  membrane  formation  by  a  fatty  acid 
starts,  therefore,  the  development  in  the  sea-urchin  egg,  but 
this  development  is  abnormal  and  the  egg  is  sickly  and  perishes 
the  more  rapidly  the  higher  the  temperature.  The  question 
arises,  how  can  we  inhibit  this  sickliness  and  grant  a  normal 
development  to  the  egg? 

I  found  that  two  different  means  are  at  our  disposal  for 
this  purpose.  The  one  which  never  fails  consists  in  putting 
the  eggs  about  twenty  minutes  after  the  artificial  membrane 
formation  into  hypertonic  sea-water  (or  any  other  hypertonic 
solution,  e.g.,  sugar  solution),  i.e.,  into  sea-water  or  any  other 
solution  the  osmotic  pressure  of  which  has  been  rendered 
50  per  cent  higher  than  that  of  the  sea-water.  In  this  solution 
the  eggs  remain  from  twenty  to  sixty  minutes — according  to 
the  temperature  and  the  concentration  of  hydroxyl-ions  in  the 
solution.  If  after  this  time  the  eggs  are  transferred  into  normal 
sea-water  they  develop  at  room  temperature  in  a  way  similar  to 
the  eggs  which  are  fertilized  by  sperm. ^ 

The  second  method  of  causing  the  eggs  to  develop  normally 
at  room  temperature  after  the  artificial  causation  of  the  mem- 
brane formation  consists  in  putting  these  eggs  for  three  hours 
in  sea-water  free  from  oxygen  or  into  sea-water  to  which  a 
trace  of  KCN  has  been  added.  After  the  eggs  are  transferred 
into  normal  sea-water  they  develop  often  but  not  always.  This 
method  is,  therefore,  not  quite  as  reliable  as  the  other  method 
mentioned  previously. 

We  see,  therefore,  that  the  formative  stimulus  in  the  artificial 
activation  of  the  egg  of  the  sea-urchin  consists  of  two  phases, 

1  The  larvae  originating  from  eggs  fertilized,  by  sperm  live  no  longer  than  those 
originating  from  eggs  which  develop  parthenogenetically,  if  the  larvae  are  not  fed. 
The  feeding  of  these  larvae  is  a  tedious  process  and  for  this  reason  I  have  not 
undertaken  the  task.  Delage  has,  however,  raised  two  such  larvae  until  they  were 
sexually  mature. 


132         The   Mechanistic  Conception  of  Life 

namely,  first  the  artificial  causation  of  the  membrane  formation 
and  second  the  subsequent  short  treatment  of  the  egg  with  a 
hypertonic  solution;  (or  a  longer  treatment  with  an  isotonic 
solution  free  from  oxygen  or  containing  KCN). 

We  may  add  that  these  observations  do  not  hold  good  for 
the  sea-urchin  egg  only.  Similar  observations  were  made  on 
the  eggs  of  annelids  (Polynoe)  and  of  star-fish  (Asterina). 
In  Polynoe  and  star-fish  the  artificial  membrane  production  is 
often  sufficient  to  allow  the  eggs  to  develop  into  larvae.  But 
the  number  of  eggs  which  reach  the  larval  stage  and  the  type 
of  segmentation  is  improved  if  the  eggs  are  treated  subsequently 
with  one  of  the  above-mentioned  methods,  as  R.  Lillie  found  for 
Asterias  and  I  for  Polynoe.  The  experiments  on  annelids  and 
star-fish,  therefore,  confirm  the  fact,  that  the  calling  forth  of 
the  membrane  is  the  essential  feature  in  formative  stimulation 
and  that  the  subsequent  treatment  of  the  eggs  with  a  hyper- 
tonic solution  (or  an  isotonic  solution  free  from  oxygen)  has 
merely  a  corrective  effect;  it  probably  counteracts  a  secondary 
detrimental  effect  connected  with  the  membrane  formation. 

Ill 

We  will  now  try  to  gain  some  insight  into  the  mechanism  of 
these  two  agencies.  How  can  the  fatty  acid  cause  the  formation 
of  a  membrane  ?  In  order  to  get  an  answer  to  this  question 
we  must  find  out  whether  there  are  other  agencies  which 
act  like  fatty  acids.  It  was  noticed  that  all  the  agencies 
which  cause  cytolysis  also  cause  membrane  formation,  namely, 
first  the  specifically  cytolytic  agencies  like  saponin,  solanin, 
digitalin,  bile  salts,  and  soaps.  Experiments  with  these  agencies, 
especially  with  saponin,  solanin,  and  digitalin,  yielded  a  curious 
result.  If  the  unfertilized  eggs  are  put  into  a  weak  solution  of 
saponin  in  sea-water  we  notice  as  the  first  effect  on  the  eggs 
the  formation  of  a  fertilization  membrane.  Then  ensues  a  pause 
of  sometimes  several  minutes  and  after  this  pause  a  sudden 


Nature  of  Formative  Stimulation 


133 


cytolysis  of  the  whole  egg  follows.     If  we  take  the  eggs  during 
this  pause  (i.e.,  after  the  membrane  is  formed,  but  before  the 


Fig.  39 


Fig.  40 


Fig.  41 


Fig.  42 


Fig.  43 


Figs.  39— i3. — Membrane  formation  and  subsequent  cytolysis  of  the  sea- 
urchin  egg  in  a  weak  solution  of  saponin  in  sea-water.  Camera  drawings  from 
nature.  Fig.  39,  unfertilized  egg  at  the  beginning  of  the  experiment.  In  this 
condition  the  egg  was  put  into  sea-water  containing  a  small  amount  of  saponin. 
The  following  figures  show  the  changes  it  imderwent  in  this  solution.  Fig.  40, 
membrane  formation  under  the  influence  of  saponin,  eight  minutes  later.  If  the 
egg  is  taken  out  of  the  saponin-sea-water  in  this  stage,  washed  and  put  into  a 
hypertonic  solution  for  about  one  half-hour,  it  will  develop  into  a  larva,  after  it  is 
put  back  into  normal  sea-water.  If,  however,  it  is  left  in  the  saponin  solution  it 
undergoes  the  rapid  cytolysis  represented  in  Figs.  41,  42,  and  43.  In  the  above 
drawing  of  the  egg,  cytolysis  began  at  G,  Fig.  41,  five  minutes  after  the  membrane 
formation.  The  stages  represented  in  Figs.  42  and  43  were  reached  a  few  minutes 
later. 


cytolysis  of  the  egg  occurs)  out  of  the  sea-water  containing 
saponin  and  free  them  from  all  traces  of  saponin  by  wash- 
ing them  repeatedly  with  sea-water,  they  behave  as   if  the 


134         The  Mechanistic  Conception  of  Life 

membrane  formation  had  been  called  forth  by  a  fatty  acid. 
Such  eggs  begin  to  develop,  but  do  not  go  beyond  the  first 
nuclear  division  at  room  temperature.  If,  however,  the  eggs 
are  treated  for  half  an  hour  with  hypertonic  sea-water  they 
can  develop  to  normal  plutei,  i.e.,  larvae  with  skeletons. 

The  second  group  of  cytolytic  agencies  is  formed  by  the 
specific  fat  solving  hydrocarbons  like  amylen,  benzol,  toluol, 
and  in  a  much  lesser  degree  chloroform,  etc.  Hertwig  had 
already  observed  that  chloroform  calls  forth  the  membrane 
formation  and  Herbst  had  seen  the  same  effect  brought  about 
by  benzol  and  toluol.  But  these  substances  act  so  violently 
that  the  membrane  formation  is  followed  almost  immediately 
by  a  cytolysis  of  the  egg,  and  for  this  reason  these  authors  could 
not  notice  that  the  membrane  formation  was  followed  by  the 
development  of  the  egg.  I  have,  however,  been  able  to  con- 
vince myself  that  if  amylen  or  benzol  are  allowed  to  act  only 
for  one  moment  and  if  the  eggs  are  then  quickly  transferred 
into  normal  sea-water  a  membrane  formation  can  be  produced  in 
some  of  them  without  subsequent  cytolysis.  If  such  eggs  were 
afterward  treated  with  hypertonic  sea-water  they  developed 
into  larvae. 

A  further  group  of  cytolytic  agencies  is  ether  or  alcohols. 
Cytolysis  of  the  eggs  by  these  agencies  is  also  preceded  by  a 
membrane  formation.  If  the  eggs  are  taken  out  from  such 
solutions  immediately  after  membrane  formation  they  can  be 
saved  from  cytolytic  destruction  (Figs.  44-47). 

Bases  can  also  call  forth  membrane  formation,  but  their 
action  is  rather  slow  and  depends  on  the  presence  of  free  oxygen. 
One  gains  the  impression  as  if  the  alkali  acted  in  this  case  only 
as  an  accelerator  of  oxidations  and  as  if  a  product  of  oxidation 
was  the  proper  cause  for  the  membrane  formation.  The 
membrane  formation  usually  becomes  manifest  only  if  one 
treats  the  eggs  afterward  for  a  short  time  with  a  hypertonic 
solution ;  such  a  treatment  causing  them  to  develop  into  larvae. 


Nature  of  Formative  Stimulation 


135 


An  increase  in  temperature  can  also  produce  a  cytolytic 
effect.  I  have  observed  that  at  34°  or  35°  the  eggs  of  Strongylo- 
centrotus  purpuratus  form  often  but  not  always  a  membrane 


Fig.  44 


Fig.  45 


Fig.  46 


Fig.  47 


Figs.  44-47. — Membrane  formation  and  subsequent  cytolysis  of  the  egg 
under  the  influence  of  the  addition  of  a  minute  quantity  of  salicylaldehyde  to 
sea-water.  Camera  drawings.  Fig.  44,  unfertilized  egg  at  the  beginning  of  the 
experiment.  Fig.  45,  membrane  formation  in  the  salicylaldehyde-sea-water. 
Fig.  46,  beginning  of  the  cytolysis.  Fig.  47,  cytolysis  completed.  The  cj-tolyzed 
egg  has  in  this  case  an  entirely  different  appearance  from  that  of  an  egg  cytolyzed 
in  saponin. 


of  fertilization.  Such  a  temperature  kills  these  eggs  almost 
instantly  and  consequently  they  are  no  longer  able  to  develop 
after  this  treatment.  The  eggs  of  the  star-fish  Asterias  for- 
hesii  are,  however,  not  killed  so  rapidly  after  the  membrane 


136         The  Mechanistic  Conception  of  Life 

formation,  and  R.  Lillie  was  able  to  show  that  such  eggs  can 
develop  into  larvae  if  the  membrane  formation  is  called  forth 
by  raising  the  temperature.  Von  Knaffl  has  shown  that  if  a 
high  temperature  acts  for  some  time  on  these  eggs  they  perish 
by  cytolysis  and  are  transformed  into  "ghosts." 

We  have  been  able  to  convince  ourselves,  therefore,  that  all 
the  agencies  which  cause  cytolysis  also  call  forth  the  membrane 
formation;  while  the  agencies  which  do  not  call  forth  cytolysis 
do  not  cause  a  membrane  formation.  We  find  in  addition  that 
the  cytolytic  power  of  these  agencies  runs  parallel  with  their 
power  of  causing  membrane  formation. 

From  this  we  draw  the  inference  that  the  membrane  forma- 
tion depends  upon  the  cytolysis  of  the  surface  layer  of  the  egg. 
We  shall  see  later  on  that  we  must  discriminate  between  a 
cortical  layer  and  the  core  of  the  unfertilized  egg.  This 
superficial  cortical  layer  of  the  egg  is  very  thin.  The  essential 
feature  of  the  developmental  stimulus  consists  in  the  cytolysis 
of  this  cortical  layer  of  the  egg  and  this  cytolysis  is  caused  by 
the  spermatozoon. 

IV 

We  have  already  mentioned  that  the  cytolysis  which  under- 
lies the  membrane  formation  causes  the  development  of  the 
egg,  but  that  the  egg  is  as  a  rule  sickly  after  this  membrane 
formation.  To  fix  our  ideas  provisionally  we  assume  that 
through  the  membrane  formation  a  substance  is  formed  which 
must  be  abolished  or  destroyed  before  the  egg  is  able  to  develop 
normally.  If  we  permit  the  egg  to  begin  its  development  while 
it  still  contains  this  hypothetical  detrimental  substance  in  a 
sufficient  quantity  it  is  sickly  and  dies  prematurely.  The 
destruction  of  this  hypothetical  substance  can  be  brought  about 
in  two  ways :  first,  by  treating  the  egg  for  a  short  time  with  a 
hypertonic  solution.  When  I  discovered  this  fact  there  was  no 
analogue  known  which  allowed  us  to  draw  an  inference  concern- 
ing the  mode  of  action  of  a  hypertonic  solution.     I  succeeded 


Nature  of  Formative  Stimulation  137 


in  showing  that  such  a  solution  is  only  effective  in  artificial 
parthenogenesis  if  it  contains  free  oxygen.  If  the  hypertonic 
solution  is  deprived  of  oxygen  it  remains  without  any  effect.  It 
remains  also  inefficient  if  a  trace  of  KCN  is  added  to  it.  Since 
KCN  inhibits  the  oxidations  in  the  cell  it  is  obvious  that  the 
hypertonic  solution  only  acts  by  a  modification  of  the  process 
of  oxidation. 

The  second  method  of  saving  the  life  of  the  egg  consists  in 
putting  it  after  the  membrane  formation  for  about  three  hours 
into  sea-water  which  is  practically  free  from  oxygen,  or  contains 
a  trace  of  KCN  whereby  the  oxidations  in  the  egg  are  suppressed. 
If  these  eggs  are  transferred  after  this  time  into  normal  sea- 
water  containing  free  oxygen  they  are  often  able  to  develop 
normally.^ 

V 

Thus  far  we  have  dealt  only  with  artificial  parthenogenesis. 
We  are  now  about  to  take  up  the  causation  of  development  by 
a  spermatozoon.  Is  the  formative  stimulation  of  the  egg  by 
spermatozoon  of  the  same  character  as  that  in  artificial  partheno- 
genesis? This  question  can  be  answered  in  the  affirmative. 
It  is  possible  to  show  that  the  spermatozoon  also  calls  forth  the 
normal  development  of  the  egg  by  at  least  two  substances  and 
that  one  of  these  substances  acts  like  butyric  acid  or  saponin 
in  artificial  parthenogenesis,  inasmuch  as  it  causes  the  cytolysis 
of  the  thin  cortical  layer  of  the  egg;  while  the  second  substance 
has  an  effect  similar  to  that  of  the  hypertonic  solution.  The 
correctness  for  this  view  is  proved  by  the  fact  that  I  succeeded 
in  separating  these  two  effects  of  the  spermatozoon. 

If  we  wish  to  bring  about  a  separation  of  these  two  agencies 
in  the  spermatozoon  we  cannot  use  the  spermatozoa  of  the 
same  species  of  sea-urchins  from  which  the  egg  is  taken;  for 
in  this  case  the  spermatozoon  penetrates  at  once  into  the 

1  a  further  discussion  of  the  facts  in  this  chapter  is  contained  in  the  next  paper 
on  "  The  Prevention  of  the  Death  of  the  Egg  through  the  Act  of  Fertilization. " 


138         The  Mechanistic  Conception  of  Life 

protoplasm  of  the  egg  as  soon  as  it  comes  in  contact  with  it. 
In  this  way  almost  simultaneously  both  substances  of  the 
spermatozoon  become  effective,  the  cytolytic  substance,  which 
causes  the  membrane  formation,  and  the  ''corrective'^ substance. 
The  experiments,  however,  result  differently  when  we  add  the 
spermatozoa  of  a  foreign  species,  e.g.,  star-fish,  to  the  egg  of 
the  sea-urchin.  Under  ordinary  conditions  sperm  of  the  star-fish 
cannot  cause  the  egg  of  the  sea-urchin  to  develop;  it  becomes 
effective,  however,  in  sea-water  which  has  been  rendered  a  little 
more  alkaline  through  the  addition  of  some  NaHO.  If  0.6  c.c. 
n/10  NaHO  is  added  to  50  c.c.  of  sea-water  all  the  eggs  of  the 
sea-urchin  form  fertilization  membranes  in  such  a  mixture  if 
only  a  trace  of  living  sperm  of  a  star-fish  (Asterias  ochracea)  is 
added.  It  takes,  however,  some  time,  mostly  from  ten  to  fifty 
minutes,  until  the  living  star-fish  sperm  brings  about  this  effect; 
while  after  the  addition  of  sea-urchin  sperm  this  result  is 
obtained  in  one  minute. 

If  the  sea-urchin  eggs,  all  of  which  have  formed  membranes 
upon  the  addition  of  living  star-fish  sperm,  are  put  back  into 
normal  sea-water  and  if  we  watch  their  further  fate,  we  soon 
notice  that  we  are  dealing  with  two  groups  of  eggs.  The  one 
group  acts  as  if  only  one  of  the  two  agencies,  namely,  the 
cytolytic  one,  had  taken  effect.  These  eggs  show  at  room 
temperature  only  the  beginning  of  nuclear  division  and  then 
disintegrate,  while  at  a  lower  temperature  they  may  develop  a 
little  farther.  If  we  treat  them,  however,  after  the  membrane 
formation  by  star-fish  sperm  for  from  thirty  to  fifty  minutes 
with  a  hypertonic  solution  they  all  develop  at  room  temperature 
mostly  into  normal  larvae.  The  other  eggs  develop  without 
any  subsequent  treatment  with  a  hypertonic  solution  into 
normal  larvae. 

What  causes  this  difference  in  the  behavior  of  both  groups 
of  eggs  ?  A  histological  examination  of  these  eggs  decides  this 
point.     My  assistant,  Mr.  Elder,  found  that  a  spermatozoon 


Nature  of  Formative  Stimulation  139 

had  entered  into  those  eggs  which  develop  after  the  addition 
of  star-fish  sperm  without  subsequent  treatment  with  a  hyper- 
tonic solution  into  normal  larvae;  while  the  eggs  which  behave 
as  if  only  an  artificial  membrane  formation  had  taken  place 
do  not  contain  any  spermatozoon. 

This  behavior  of  the  eggs  under  the  influence  of  foreign 
sperm  is  comprehensible  under  the  assumption  that  the 
spermatozoon  also  causes  the  development  of  the  egg  through 
two  agencies;  one  of  these  agencies  is  a  cytolytic  substance, 
a  so-called  lysin.  This  substance  is  probably  situated  at  the 
surface  of  the  spermatozoon.  This  lysin  only  calls  forth 
the  membrane  formation  and  it  acts  like  the  butjrric  acid  in 
the  method  of  artificial  parthenogenesis.  The  second  agency 
seems  to  be  more  in  the  interior  of  the  spermatozoon  and  it 
exercises  an  influence  similar  to  the  short  treatment  of  the  egg 
with  a  hypertonic  solution.  A  normal  development  will  result 
only  if  the  spermatozoon  enters  the  egg  since  in  this  case  only 
both  agencies,  the  cytolytic  and  the  corrective,  get  into  the 
egg.  We  have  already  mentioned  that  foreign  spermatozoa 
penetrate  only  slowly  into  the  egg.  If  a  spermatozoon  pene- 
trates partially  through  the  surface  of  the  egg  without  entirely 
penetrating  into  the  protoplasm,  enough  of  the  lysin  sticking 
to  the  surface  of  the  spermatozoon  can  be  dissolved  to  cause 
the  cytolysis  of  the  surface  film  of  the  egg  which  gives  rise  to  the 
membrane  formation.  Such  eggs  receive  from  the  spermato- 
zoon only  the  lysin,  and  they  act  therefore  as  if  only  the  mem- 
brane formation  had  been  called  forth  in  them  by  the  treatment 
with  butyric  acid,  since  in  the  formation  of  the  membrane 
the  spermatozoon  is  thrown  out. 

In  the  eggs  of  Strongylocentrotus  purpuratus  the  mem- 
brane formation  can  in  general  only  be  called  forth  by  living 
star-fish  sperm  while  the  extract  of  dead  star-fish  sperm  in  the 
same  concentration  remains  without  effect.  This  fact  is  of  im- 
portance to  disprove  the  possibility  that  the  membrane  formation 


140         The  Mechanistic  Conception  of  Life 

in  these  experiments  was  caused  by  star-fish  blood  which  was 
added  with  the  sperm. 

That  it  is  possible  to  separate  a  lysin  from  the  sperm  can 
be  proved  for  the  eggs  of  another  species  of  sea-urchins,  namely, 
Strongylocentrotus  frandscanus,  the  eggs  of  which  are  very 
sensitive  to  lysins.  In  these  eggs  it  is  possible  to  call  forth  the 
membrane  formation  with  a  very  dilute  watery  extract  of  the 
sperm  of  star-fish  which  was  killed  by  heating  it  to  60°  C,  or 
more.  Such  eggs  can  be  caused  to  develop  into  plutei  by  treat- 
ing them  after  the  membrane  formation  for  a  short  time  with 
hypertonic  sea-water.  In  the  place  of  star-fish  sperm  the 
sperm  of  other  foreign  species  can  be  used.  I  have  called  forth 
the  membrane  formation  in  the  sea-urchin  egg  with  the  living 
sperm  of  sharks  or  even  roosters.  Such  eggs  act  as  if  only  the 
membrane  formation  with  the  aid  of  butyric  acid  had  been 
caused.  At  room  temperature  they  begin  to  develop  but  they 
are  sickly  and  soon  perish.  If,  however,  they  are  treated 
afterward  with  a  hypertonic  solution  they  develop  into  normal 
plutei.  In  this  case  only  the  lysin  entered  the  egg  but  not  the 
spermatozoon.  It  was,  therefore,  necessary  to  treat  such  eggs 
subsequently  with  hypertonic  sea-water  in  order  to  cause  them 
to  undergo  normal  development  at  room  temperature. 

VI 

The  idea  that  a  lysin  contained  in  the  spermatozoon  is  the 
formative  stimulus  which  causes  the  egg  to  develop  can  be 
tested  experimentally.  We  know  that  blood  contains  lysins 
which  destroy  the  blood  corpuscles  of  foreign  species,  while 
it  does  not  destroy  the  cells  of  the  same  species.  If  the  idea  is 
correct  that  the  spermatozoon  acts  upon  the  egg  through  a 
lysin  which  calls  forth  the  membrane  formation  it  should  be 
possible  to  call  forth  the  membrane  formation  in  the  unferti- 
lized egg  of  the  sea-urchin  by  foreign  blood  and  such  is  the  case. 
I  was  able  to  show  three  years  ago  that  the  blood  of  certain 


Nature  of  Formative  Stimulation  141 

worms,  namely  SipuncuUdes ,  can  call  forth  the  membrane 
formation  in  the  sea-urchin  egg  even  if  it  is  diluted  a  hundred 
times  or  more  with  sea-water.  This  effect  is  not  produced 
in  the  eggs  of  every  female  sea-urchin  but  of  only  about  20 
per  cent  of  the  females.  I  think  the  difference  is  caused  by 
differences  in  the  permeability  of  the  eggs  for  lysins;  and  the 
degree  of  permeability  seems  to  vary  slightly  for  the  eggs  of 
different  females. 

Instead  of  wasting  time  on  an  examination  of  the  effects  of 
the  blood  of  invertebrates^  I  examined  the  effects  of  the  blood 
serum  of  warm-blooded  animals.  I  succeeded  in  causing 
membrane  formation  in  the  sea-urchin  egg  (purpuratus)  with  the 
blood  serum  of  cattle,  sheep,  pigs,  and  rabbits;  and  such  eggs 
behaved  like  the  eggs  which  had  been  treated  with  the  living 
sperm  of  roosters  or  with  butyric  acid.  They  began  to  develop, 
but  they  became  sickly  at  room  temperature  and  soon  disinte- 
grated. If,  however,  they  were  treated  after  the  membrane 
formation  for  a  short  time  with  a  hypertonic  solution  they 
developed  at  room  temperature.  The  blood,  therefore,  contains 
the  lysin,  but  not  the  second  substance  necessary  for  the 
full  development.  It  is,  therefore,  necessary  to  substitute  for 
the  action  of  the  latter  the  treatment  with  a  hypertonic  solu- 
tion if  we  wish  to  call  forth  a  normal  development  of  the  egg 
treated  with  serum. 

The  lysin  of  the  blood  is  like  that  of  the  spermatozoon 
relatively  resistant  to  heat.  The  blood  does  not  lose  its  power 
to  call  forth  membrane  formation  by  heating  it  for  some  time  to 
60°  or  65°  C.2  It  is  curious  that  SrCla  and  Babla  increase  the 
membrane-forming  power  of  the  blood. 

Not  only  blood  but  also  the  extracts  of  the  organs  of  foreign 

1  Since  this  was  written  the  blood  and.  the  extracts  of  organs  of  a  number  of 
invertebrates  were  used  successfully  to  produce  the  membrane  formation  and 
development  of  the  egg  of  the  sea-urchin. 

2  The  substance  which  cavises  membrane  formation  can  be  precipitated  with 
acetone  (Loeb,  Pflugers  Archiv,  CXXIV,  37,  1908). 


142         The   Mechanistic  Conception  of  Life 

species  call  forth  membrane  formation  in  the  sea-urchin  egg. 
An  extract  of  the  coecum  of  the  star-fish  was  very  effective. 

We  have  already  mentioned  the  fact  that  the  extract  of 
dead  sperm  of  foreign  species,  e.g.,  of  star-fish,  certain  mollusks, 
certain  worms,  sharks,  fowl,  causes  membrane  formation  in  the 
eggs  of  franciscanus.  Experiments  with  the  extract  of  dead 
sperm  of  their  own  species  on  the  egg  oi  franciscanus  or  purpura- 
tus  fail;  and  the  same  is  true  for  extracts  from  the  tissues  of 
these  species.^  What  causes  this  difference  in  the  action  of 
the  lysins  from  their  own  and  a  foreign  species?  We  know 
that  the  lysins  of  our  own  blood  do  not  hurt  our  cells  while 
they  hurt  the  cells  of  foreign  species.  There  exists,  therefore, 
an  immunity  of  the  eggs  as  well  as  of  the  rest  of  the  cells  against 
the  lysins  of  their  own  blood  or  tissues. 

Our  experiments  throw  a  light  upon  the  nature  of  this 
immunity.  If  the  lysins  contained  in  our  blood  do  not  injure 
our  cells  it  can  only  be  due  to  one  of  two  facts:  The  lysins  of 
our  own  blood  can  either  not  diffuse  into  our  cells,  while  they 
can  diffuse  into  the  cells  of  foreign  forms,  or  the  cells  contain 
antibodies  against  the  lysins  of  their  own  body,  but  not  against 
those  of  foreign  species.  As  far  as  the  lysins  of  the  blood  are 
concerned  we  cannot  decide  between  the  two  possibilities. 
We  can,  however,  reach  a  decision  for  the  lysins  of  the  sperma- 
tozoa. The  extract  from  the  dead  sperm  of  the  sea-urchin  is 
ineffective  for  the  eggs  of  the  sea-urchin  solely  for  the  reason 
that  it  cannot  diffuse  into  the  sea-urchin  egg.  For  if  the  sea- 
urchin  lysin  is  carried  by  the  living  sea-urchin  spermatozoon 
(which  acts  as  a  motor  for  the  lysin)  into  the  sea-urchin  egg, 
the  lysin  is  very  active  and  probably  more  active  than  the 
lysin  of  foreign  species.  If  the  sea-urchin  egg  contained  an 
antibody  against  the  lysin  of  the  sea-urchin  sperm,  the  sea- 
urchin  sperm  should  not  be  able  to  call  forth  membrane 
formation  when  it  enters  the  sea-urchin  egg. 

1  If  eggs  were  sensitized  with  SrCl^  they  could  be  caused  to  develop  by 
extracts  from  the  coecum  of  the  sea-urchin,  though  this  was  true  only  exceptionally. 


Nature  of  Formative  Stimulation  143 

We  now  understand  the  paradoxical  fact,  that  by  foreign 
sperm  we  can  cause  membrane  formation  and  development  of 
the  sea-urchin  egg  in  two  different  ways:  namely,  first  by  the 
living  sperm  and  second  by  the  extract  from  the  dead  sperm; 
while  the  sperm  of  the  same  species  can  only  cause  the  eggs  to 
develop  when  it  is  alive.  We  now  understand  the  fact  alluded 
to  at  the  beginning  of  this  chapter  that  my  first  experiments 
to  cause  the  development  of  the  egg  with  extract  of  sperm  did 
not  succeed,  since  I  took  it  for  granted  that  it  was  necessary 
to  use  the  extract  of  the  sperm  of  the  same  species  from  which 
the  eggs  were  taken.  The  lysins  in  this  case  were  not  able  to 
diffuse  into  the  egg. 

The  further  unraveling  of  the  nature  of  the  immunity  of  the 
egg-cell  against  the  dissolved  lysins  of  the  blood  and  the  tissues 
of  the  same  species  depends  upon  the  explanation  of  the  fact 
that  the  lysins  of  a  species  cannot  diffuse  into  the  egg  of  the 
same  species.  It  would  be  of  interest  if  the  same  principle 
formed  for  the  immunity  of  the  egg-cell  would  hold  also  for  the 
immunity  of  the  body-cells  against  the  lysins  in  the  blood  of 
their  own  species. 

We  may,  therefore,  say  that  the  substance  to  which  the 
sperm  owes  its  fertilizing  power  is  a  lysin  and  we  may  express 
the  suspicion  that  the  lysins  which  we  have  thus  far  known 
only  as  protective  agencies  against  bacteria  play  a  great  physio- 
logical role  in  the  mechanism  of  life  phenomena.  We  may  call 
our  theory  of  the  developmental  action  of  the  spermatozoon 
the  lysin  theory;  thereby  designating  that  the  impulse  for  the 
development  of  the  egg  is  given  by  a  lysin  contained  in  the 
spermatozoon.  In  artificial  parthenogenesis  we  substitute  for 
the  natural  lysin  a  cytolytic  substance.  Aside  from  the  lysin 
action  the  normal  development  demands,  as  a  rule  (but  not 
always),  a  second  corrective  influence  which  in  artificial  par- 
thenogenesis may  be  given  by  a  hypertonic  solution. 


144         The   Mechanistic  Conception  of  Life 

VII 

The  experiments  on  the  artificial  parthenogenesis  of  other 
forms  of  animals  show  that  the  eggs  of  different  animals  possess 
a  varying  tendency  for  parthenogenetic  development.  There 
are  eggs  which  can  easily  be  induced  to  develop,  so  easily  in 
fact,  that  the  experimenter  cannot  always  be  sure  whether  he 
has  caused  the  development  by  a  substance  applied  by  him  or 
whether  some  accidental  condition  of  the  experiment  was 
responsible.  The  eggs  of  the  silkworm,  of  the  star-fish,  and 
of  certain  worms  belong  to  this  class.  In  working  with  star- 
fish eggs  we  can  observe  that  occasionally  a  few  of  them  develop 
in  normal  sea-water,  apparently  without  any  demonstrable 
cause,  into  swimming  larvae.  The  eggs  of  the  Calif ornian 
sea-urchin  Strongylocentrotus  purpuratus,  on  the  other  hand, 
show  not  the  slightest  tendency  to  segment  parthenogenetically ; 
only  the  above-mentioned  very  specific  and  quantitative  method 
causes  them  to  develop.  For  this  reason  I  selected  these  eggs 
for  the  investigation  of  the  nature  of  the  experimental  stimulus, 
since  I  could  always  be  sure  that  the  same  stimulus  gave  the 
same  results;  while,  e.g.,  in  the  star-fish  eggs  we  can  never  be 
perfectly  certain  that  some  internal  condition  in  the  egg  or  some 
overlooked  unimportant  secondary  condition  in  the  experiment 
may  not  have  caused  the  development.  Although  eggs  with 
such  a  strong  tendency  for  spontaneous  development  as  the 
star-fish  eggs  are  not  the  best  material  for  the  study  of  the 
nature  of  the  developmental  stimulus  yet  we  have  to  answer 
the  question  how  it  happens  that  some  eggs  have  a  greater 
tendency  for  parthenogenetic  development  than  others. 

Mathews  has  observed  that  by  gently  shaking  the  star-fish 
eggs  the  number  of  eggs  which  develop  ''spontaneously"  can 
be  increased.  I  made  a  similar  observation  in  the  eggs  of 
Amphitrite,  an  annelid.  In  the  eggs  of  the  sea-urchin  nobody 
has  ever  been  able  to  obtain  such  a  result.  I  am  inclined  to 
believe  that  if  a  sea-urchin  should  be  found,  the  eggs  of  which 


Nature  of  Formative  Stimulation  145 


possess  a  greater  tendency  to  develop  spontaneously,  it  might 
also  be  found  that  the  number  of  eggs  developing  spontaneously 
might  be  increased  by  agitation. 

I  tried  whether  it  is  possible  to  cause  the  eggs  to  cytolyze 
also  mechanically.  If  we  exercise  only  a  slight  pressure  with 
a  finger  upon  the  ovary  of  a  star-fish  we  find  that  many  of 
the  eggs  which  afterward  leave  the  ovary  are  cytolyzed.  This 
cytolysis  is  not  caused  by  a  bursting  of  the  egg  membrane;  on 
the  contrary,  in  this  case  the  cytolysis  of  the  egg  is,  as  usual, 
preceded  by  the  formation  of  a  membrane  of  fertilization  and 
this  membrane  remains  intact  in  the  star-fish  egg  which  is 
caused  to  cytolyze  by  mechanical  pressure.  In  the  sea-urchin 
egg,  however,  it  is  impossible  to  produce  cytolysis  by  a  slight 
pressure. 

The  eggs  of  the  star-fish  which  develop  spontaneously  first 
form  a  membrane.  Shaking  causes  a  development  of  the  star- 
fish eggs  only  if  the  shaking  first  leads  to  a  membrane  formation. 
The  greater  tendency  of  the  star-fish  to  develop  spontaneously 
is,  therefore,  due  to  the  greater  ease  with  which  cytolysis  can 
be  produced  in  this  egg. 

How  can  mere  agitation  or  pressure  call  forth  membrane 
formation  or  cytolysis  ?  It  seems  to  me  that  this  fact  is  most 
easily  understood  under  the  assumption,  first  suggested  by 
Blitschli,  that  the  cytoplasm  is  an  emulsion.  It  would  then 
follow  that  the  membrane  formation  as  well  as  the  cytolysis 
depends  upon  the  destruction  of  this  emulsion.  We  know  that 
different  emulsions  have  a  different  degree  of  durability.  The 
eggs  which  upon  gentle  pressure  undergo  cytolysis  have  an 
emulsion  with  a  lesser  degree  of  durability  than  the  eggs  in  which 
pressure  has  no  such  effect.  Let  us  assume  that  membrane 
formation  as  well  as  cytolysis  depends  upon  the  destruction 
of  an  emulsion;  in  this  case  the  membrane  formation  depends 
upon  the  destruction  of  the  emulsion  in  the  cortical  layer  of  the 
egg  only.     The  lysin  of  the  egg  destroys  only  the  emulsion  in 


146         The  Mechanistic  Conception  of  Life 

the  cortical  layer  of  the  egg  and  thereby  causes  development. 
The  greater  tendency  of  the  eggs  of  certain  animals  for  spon- 
taneous parthenogenetic  development  thus  depends  upon  the 
relatively  small  degree  of  durability  of  the  emulsion  which 
constitutes  the  cortical  layer  of  the  egg.  But  it  should  be 
stated  that  this  hypothesis  is  not  essential  for  the  lysin  theory 
of  the  activation  of  the  egg. 

VIII 

The  assumption  that  the  membrane  formation  is  only  a 
superficial  cjrfcolysis  of  the  egg  presupposes  that  the  cortical 
layer  of  the  egg  is  different  from  the  rest  of  the  cytoplasm. 
Biitschli  had  already  reached  such  a  conclusion  on  the  basis 
of  histological  observations.  I  am  inclined  to  accept  this  view 
on  the  basis  of  my  observations  on  the  action  of  cytolytic 
agencies  on  the  unfertilized  egg.  The  action  of  these  agencies 
on  the  unfertilized  egg  always  occurs  in  two  stages  which  are 
often  separated  from  each  other  by  a  considerable  interval  of 
time.  The  first  stage  is  the  cytolysis  of  the  superficial  layer; 
the  second  stage  is  the  cytolysis  of  the  rest  of  the  egg.  This 
is  -most  obvious  in  experiments  with  weak  solutions  of  saponin 
or  solanin  in  sea-water.  In  this  case  first  a  membrane  forma- 
tion occurs,  then  a  pause  ensues,  often  of  several  minutes,  and 
then  cytolysis  of  the  whole  egg  follows.  If  instead  of  saponin 
benzol  is  used  a  pause  can  also  be  observed  between  membrane 
formation  and  cytolysis  of  the  whole  egg  but  this  pause  is  short, 
often  only  a  fraction  of  a  second,  or  at  the  best  a  few  seconds. 

It  can  also  be  shown  directly  that  there  is  a  qualitative 
difference  between  the  cortical  layer  of  the  protoplasm  and  the 
rest.  If  for  the  artificial  membrane  formation  the  lower  fatty 
acids,  from  the  formic  to  the  capronic  acid,  are  used,  cytolysis 
of  the  cortical  layer  only  is  observed,  i.e.,  membrane  formation 
follows  but  no  cytolysis  of  the  whole  egg.  If,  however,  the 
higher  fatty  acids  of  the  same  series  from  the  heptylic  acid  on 


Nature  of  Formative  Stimulation  147 

and  upward  are  applied  the  membrane  formation  is  always 
followed  after  a  short  pause  by  a  cytolysis  of  the  whole  egg. 

The  lysins  contained  in  the  blood  and  the  spermatozoon 
act  according  to  my  present  experience  only  upon  the  cortical 
layer  of  the  cytoplasm  but  not  on  the  rest  of  the  egg.  We  get  a 
membrane  formation  and  development  but  not  a  cytolysis  of 
the  whole  egg. 

If  we  go  back  to  the  idea  of  Biitschli  that  protoplasm  has 
the  structure  of  an  emulsion  we  are  led  to  the  view  that  the 
emulsion  of  the  cortical  layer  of  the  egg  differs  from  that  of  the 
rest  of  the  egg.  There  are  certain  cytolytic  agencies  which 
destroy  only  the  cortical  layer;  while  all  general  cytolytic 
agencies  destroy  the  cortical  layer  as  well  as  the  rest  of  the  egg. 

IX 

How  can  the  cytolysis  of  the  cortical  layer  of  the  egg  lead 
to  a  membrane  formation?  Von  Knaffl  has  expressed  the 
following  view  on  this  point:  ''Protoplasm  is  rich  in  lipoids, 
it  is  probably  mainly  an  emulsion  of  these  and  of  proteins. 
Every  physical  and  chemical  agency  which  is  able  to  liquefy 
lipoids  calls  forth  a  cytolysis  of  the  egg.  The  protein  of  the 
egg  can  only  swell  or  be  dissolved  if  the  state  of  the  lipoids  is 
altered  by  chemical  or  physical  means.  The  mechanism  of 
cjrtolysis  consists  in  the  liquefaction  of  the  lipoids  and  the 
subsequent  swelling  or  liquefaction  of  proteins  by  absorption 

of  water This  confirms  Loeb's  view  that  membrane 

formation  is  caused  by  the  liquefaction  of  lipoids." 

We  can  accept  this  with  a  slight  modification  which  refers 
to  the  nature  of  the  emulsion.  An  emulsion  requires  not  only 
two  substances  or  phases  as  von  Knaffi  assumes  but  in  addition 
a  third  substance.  The  third  substance  serves  the  purpose  of 
making  the  emulsion  more  durable  (Lord  Rayleigh's  theory). 
The  droplets  of  the  emulsion  are  surrounded  by  a  thin  layer 
of  a  substance  which  lessens  the  surface  tension  between  the 


148         The  Mechanistic  Conception  of  Life 

droplet  and  the  second  phase  of  the  emulsion.  I  assume  that 
only  this  stabilizing  substance  consists  of  lipoids,  especially 
cholesterin.  The  two  other  phases  which  constitute  the 
emulsion  need  not  be  lipoids.  To  fix  our  ideas  provisionally 
we  may  assume  that  these  phases  are  first  protein  with  little 
water  and  second  water  with  little  protein.  The  existence  of 
these  two  phases  has  been  established  by  Hardy.  The  emulsion 
at  the  surface  of  the  egg  consists,  according  to  this  view,  of  a 
system  of  protein  droplets  poor  in  water  surrounded  by  a 
stabilizing  film  of  a  lipoid  (cholesterin  or  lecithin).  If  the  sea- 
urchin  egg  is  treated  with  a  lipoid  solvent  like  benzol  the 
stabilizing  film  of  cholesterin  is  dissolved  and  the  protein  drop- 
let can  absorb  water.  If  we  use  saponin  the  film  is  destroyed 
by  the  precipitation  of  cholesterin  by  saponin.  The  absorp- 
tion of  water  leads  to  the  lifting  up  of  the  surface  film  which 
surrounds  the  egg.^ 

We  wish  to  add  a  few  remarks  concerning  the  nature  of  this 
surface  film,  although  this  does  not  belong  to  our  problem. 
According  to  Overton  and  Koeppe  the  surface  film  of  cells 
consists  of  lipoids,  and  according  to  Koeppe  cytolysis  is  deter- 
mined by  the  solution  or  tearing  of  this  film.  This  view  is  not 
tenable,  since  the  surface  film  which  is  lifted  off  in  the  form  of 
the  fertilization  membrane  does  not  consist  of  a  lipoid  but  of 
protein.  This  is  suggested  by  the  fact  that  this  membrane  is 
absolutely  insoluble  in  any  lipoid  solvent.  Moreover,  this 
membrane  remains  perfectly  intact  when  the  egg  is  transformed 
into  a  "ghost." 

X 

Since  we  can  cause  the  formation  of  a  membrane  of  fertili- 
zation in  the  star-fish  egg  by  gentle  agitation  or  mere  pressure, 

1  We  have  assumed  here  that  the  fertiUzation  membrane  is  preformed  in  the 
unfertilized  egg  and  lifted  up  in  consequence  of  the  cytolysis  of  the  layer  beneath 
it.  As  I  stated  in  my  book  on  Die  chemische  Entwicklungserregung  des  tierischen 
Eies,  it  is  also  possible  that  the  fertilization  membrane  is  a  membrane  of  precipita- 
tion formed  through  the  reaction  of  a  constituent  of  the  liquefied  cortical  layer 
with  a  constituent  of  the  sea- water  (Ca?).  It  is  immaterial  for  the  problem 
discussed  in  this  paper  which  view  we  adopt  temporarily. 


Nature  of  Formative  Stimulation  149 

this  membrane  is  apparently  preformed  in  the  mifertilized  egg; 
and  if  this  be  true  the  process  of  membrane  formation  must 
consist  in  the  lifting  up  of  a  preformed  film  from  the  underlying 
cytoplasm  through  the  entrance  of  sea-water  between  this  film 
and  the  cytoplasm.  In  this  process  the  surface  film  undergoes 
a  change,  since  the  spermatozoon  can  enter  into  the  egg  before 
but  not  after  the  membrane  formation.  That  merely  a  change 
in  the  nature  of  the  surface  film  prevents  the  entrance  of  a 
spermatozoon  into  the  egg  after  the  membrane  formation  can 
be  proved  by  the  fact  that  if  we  tear  the  membrane  mechanically 
a  spermatozoon  can  penetrate  into  the  egg.  This  proves  that 
the  surface  film,  even  if  it  is  already  preformed  in  the  unferti- 
lized egg,  has  different  qualities  or  a  different  structure  when  it  is 
in  close  contact  with  the  cytoplasm  than  when  it  is  lifted  off 
from  the  cytoplasm  by  a  layer  of  sea-water. 

We  have  assumed  that  the  membrane  formation  is  deter- 
mined by  the  action  of  a  lysin  or  cytolytic  agency  upon  the 
cortical  layer  of  the  egg,  whereby  a  protein  in  this  layer  absorbs 
sea-water,  and  is  thereby  dissolved.  This  assumption  leads  to 
two  consequences:  first  it  must  be  possible  to  show  that  the 
fertilization  membrane  is  permeable  for  sea-water  and  crystal- 
loid substances  but  impermeable  for  colloids.  The  correctness 
of  this  view  can  be  proved.  If  we  add  to  the  sea-water,  con- 
taining eggs  with  a  fertilization  membrane,  a  certain  quantity 
of  dissolved  white  of  egg,  tannin,  or  blood  serum,  the  membrane 
collapses  and  closes  tight  around  the  cytoplasm.  The  reason 
is  that  almost  all  the  liquid  which  existed  between  the  mem- 
brane and  the  cytoplasm  diffused  into  the  surrounding  sea- 
water.  If  the  eggs  are  brought  back  into  normal  sea-water 
(free  from  protein)  it  diffuses  again  into  the  space  between 
the  membrane  and  the  cytoplasm,  and  the  fertilization  mem- 
brane resumes  its  former  distance  from  the  cytoplasm  and 
its  round  shape.  The  membrane  is,  therefore,  impermeable 
for  the  colloids  dissolved  in  sea-water. 


150         The  Mechanistic  Conception  of  Life 

If  salts  are  added  to  the  sea-water  or  if  it  is  diluted  by 
the  addition  of  distilled  water  the  tension  and  the  diameter 
of  the  membrane  do  not  change.  This  proves  that  the 
membrane  is  permeable  for  salts,  but  not  for  colloids,  and  that 
the  lifting  up  of  the  fertilization  membrane  is  determined  by 
the  swelling  and  subsequent  liquefaction  of  a  colloid.  This 
dissolved  colloid  exercises  an  osmotic  or  colloidal  pressure  and 
sea-water  must  diffuse  from  the  outside  under  the  fertilization 
membrane  of  the  egg  until  the  tension  of  this  membrane  equals 
the  osmotic  or  colloidal  pressure  of  the  dissolved  colloid.  This 
explains  also  why  it  is  that  the  fertilization  membrane  as  a  rule 
assumes  a  spherical  shape. 

We  now  can  understand  why  not  in  all  cases  of  fertilization 
a  distinct  fertilization  membrane  is  formed.  This  may  be  due 
to  the  fact  that  the  degree  of  swelling  of  the  colloid  of  the  cortical 
layer  varies  under  different  conditions. 

XI 

We  now  possess  a  pretty  complete  picture  of  what  happens 
to  the  egg  in  the  case  of  ''formative  stimulation,"  i.e.,  when  it 
is  caused  to  develop.  Through  a  lysin  or  some  other  cytolytic 
agency  a  certain  substance  of  the  cortical  layer,  presumably  a 
lipoid,  is  dissolved  or  precipitated,  whereby  a  protein  substance 
of  that  layer  is  able  to  absorb  water  and  swell.  Formerly  it 
was  thought  that  the  spermatozoon  caused  the  development 
of  the  egg  by  carrying  a  ferment  or  enzyme  into  it  and  that  this 
ferment  set  the  mechanism  of  development  into  action.  Others 
expressed  the  opinion  that  the  entrance  of  the  sperm  nucleus  or 
of  a  centrosome  was  responsible  for  the  development.  We  see, 
however,  that  it  suffices  to  call  forth  the  artificial  membrane 
formation  in  the  unfertilized  sea-urchin  egg,  in  order  to  observe 
after  two  or  three  hours  the  formation  of  normal  astrospheres  or 
spindles.  This  disproves  the  suggestion  that  the  fusion  of  egg 
and  sperm  nucleus  is  essential  for  the  development  of  the  egg.^ 

1  The  fusion  of  the  nuclei  is  of  course  of  importance  for  the  transmission  of 
paternal  qualities. 


Nature  of  Formative  Stimulation  151 

The  ferment  theory  of  the  activation  of  the  egg  by  the  sperma- 
tozoon is  also  wrong.  If  it  were  correct  the  velocity  of  develop- 
ment should  be  accelerated  if  not  doubled  if  two  spermatozoa 
enter  the  egg  instead  of  one;  or  if  fertilization  by  sperm  and 
artificial  parthenogenesis  are  superposed  in  the  same  egg.  But 
this  is  not  the  case.  In  neither  case  is  a  shortening  of  the 
time  which  elapses  between  two  successive  periods  of  segmen- 
tation observed.^ 

The  further  development  will  be  connected  with  the  ques- 
tion how  can  the  cytolysis  of  the  cortical  layer  of  the  egg  lead 
to  its  development?  I  may  mention  the  possibility  that  the 
cytolysis  of  the  cortical  layer  facilitates  the  diffusion  of  oxygen 
or  of  HO  ions  (bases)  or  other  substances,  necessary  for  the 
development,  into  the  egg. 

XII 

Let  us  summarize  our  results  concerning  the  activation  or 
formative  stimulation  of  the  egg.  For  the  normal  development 
at  least  two  agencies  are  required:  the  one  is  the  cytolysis  of 
the  thin  cortical  layer  of  the  egg.  Any  agency  which  causes 
this  cytolysis  (without  causing  the  cytolysis  of  the  rest  of  the 
egg)  induces  development.  The  spermatozoon  as  well  as  the 
blood  and  the  tissues  contain  a  substance  (lysin)  which  causes 
only  cytolysis  of  the  cortical  layer.  The  lower  fatty  acids, 
from  formic  to  capronic,  cause  only  the  cytolysis  of  the  cortical 
layer.  Since  most  cytolytic  agencies  cause  a  cytolysis  of  the 
whole  egg  they  can  be  used  only  if  the  eggs  are  withdrawn 
from  their  influence  after  the  cortical  layer  is  destroyed  but 
before  the  rest  of  the  egg  has  undergone  destruction. 

Cytolysis  of  the  cortical  layer  leads  often  but  not  always  to 
the  formation  of  the  membrane  of  fertilization. 

Since  all  cytolytic  substances  are  lipoid  soluble  (or  destroy 
lipoids)  it  is  probable,  but  not  proved,  that  the  formative 

1  Another  reason  is  that  the  velocity  of  segmentation  is  purely  determined 
by  the  egg,  no  matter  what  is  the  nature  of  the  spermatozoon. 


152         The  Mechanistic  Conception  of  Life 

stimulus  in  the  activation  of  the  egg  consists  in  a  liquefaction 
or  precipitation  or  some  other  modification  of  the  lipoids  of  the 
cortical  layer  of  the  egg  which  results  in  an  imbibition  or  solu- 
tion of  a  colloidal  substance  of  the  cortical  layer.  If  the  cyto- 
plasm has  the  structure  of  an  emulsion  it  is  possible  that  lipoids 
form  the  stabilizing  envelope  for  the  droplets  which,  according 
to  Lord  Rayleigh,  is  necessary  for  the  durability  of  the  emulsion. 
The  cytolysis  of  the  cortical  layer  of  the  egg  causes  its 
development,  but  this  development  is  often  abnormal  and  comes 
prematurely  to  a  standstill.  In  order  to  induce  a  more  normal 
type  of  development  a  second  agency  is  often  required,  the 
mode  of  action  of  which  is  not  yet  so  clearly  understood  as  that 
of  the  cytolytic  agency,  namely,  a  short  treatment  of  the  egg 
with  a  hypertonic  solution  containing  oxygen  or  a  longer  inhi- 
bition of  the  development  of  the  egg  in  normal  sea-water  which 
is  free  from  oxygen.  The  spermatozoon  carries  in  addition 
to  the  lysin  a  second  substance  into  the  egg,  which  acts 
similarly  to  the  hjrpertonic  solution  in  our  method  of  artificial 
parthenogenesis. 


VIII.     THE  PREVENTION  OF  THE  DEATH  OF  THE 
EGG  THROUGH  THE  ACT  OF  FERTILIZATION 


VIII 

THE  PREVENTION  OF  THE  DEATH  OF  THE  EGG 
THROUGH  THE  ACT  OF  FERTILIZATION^ 

I 

The  unfertilized  egg  dies  in  a  comparatively  short  time, 
while  the  act  of  fertilization  gives  rise  to  a  series  of  generations 
which,  theoretically  at  least,  is  of  infinite  duration.  The  act 
of  fertilization  is,  therefore,  a  life-saving  act  for  the  egg.  The 
question  arises,  in  which  way  can  the  spermatozoon  save  the 
life  of  the  egg  ? 

If  the  ovaries  of  a  star-fish  are  put  into  sea-water  the  eggs 
are  shed.  They  are  generally  immature,  and  in  this  condition 
they  caimot  be  fertilized,  either  by  spermatozoa  or  by  chemical 
means.  If  they  remain,  however,  for  some  time  in  sea-water, 
all  or  a  number  of  them  gradually  become  mature ;  that  is  to  say, 
their  nuclear  mass  is  diminished  by  the  extrusion  of  the  two 
so-called  polar  bodies.  If  immediately  after  the  extrusion  of 
the  polar  bodies  sperm  is  added,  the  eggs  develop.  They  can 
at  that  period  likewise  be  caused  to  develop  by  certain  chemical 
and  physical  agencies. 

Ten  years  ago  I  made  the  following  observations.  If  the 
eggs  are  not  caused  to  develop  by  sperm  or  by  physico-chemical 
agencies,  they  perish  very  rapidly.  At  summer  temperature 
they  may  die  in  from  four  to  six  hours.  The  death  of  the  egg 
manifests  itself  morphologically  in  a  darkening  and  blackening 
of  the  otherwise  clear  egg.  I  found  that  the  death  of  the  egg 
can  be  prevented  by  withdrawing  the  oxygen,  or  by  diminish- 
ing the  rate  of  oxidations  in  the  egg  through  the  addition  of  a 
trace  of  potassium  cyanide.     The  life-saving  action  of  lack  of 

1  Reprinted  from  the  Harvey  Lectures,  1911,  by  courtesy  of  Messrs.  J.  B. 
Lippincott  &  Co. 

155 


156         The   Mechanistic  Conception  of  Life 

oxygen  can  be  shown  in  various  ways.  The  maturation  of  the 
egg  itself  depends  upon  oxidations.  If  the  oxygen  is  withheld 
from  the  immature  eggs,  or  if  the  oxidations  in  the  immature 
eggs  are  inhibited  by  potassium  cyanide,  the  process  of  matura- 
tion does  not  take  place.  Maturation  is,  therefore,  also  a 
function  of  oxidations.  The  eggs  of  a  female,  which  were 
unripe,  were  divided  into  two  groups :  the  one  group  remained 
in  sea- water  in  contact  with  oxygen;  the  other  was  put  into 
sea-water  whose  oxygen  had  been  removed  by  a  current  of 
hydrogen.  The  eggs  of  the  second  group  remained  alive;  the 
eggs  of  the  first  group  perished  in  a  few  hours. 

It  is  not  even  necessary  to  drive  out  the  air  by  hydrogen; 
the  life  of  the  unfertilized  eggs  can  also  be  preserved  by  putting 
large  masses  of  them  into  a  narrow  glass  tube  which  is  sealed 
at  the  bottom.  The  eggs  sink  to  the  bottom  of  the  tube,  and 
those  which  are  lying  near  the  bottom  receive  no  oxygen,  since 
the  oxygen  which  diffuses  from  the  air  through  the  sea-water 
is  consumed  by  the  uppermost  layer  of  the  eggs.  On  account 
of  this  lack  of  oxygen  the  eggs  at  the  bottom  of  the  tube  do  not 
mature  and  do  not  perish;  hence  by  withholding  oxygen  from 
the  immature  eggs  their  maturation  and  death  are  prevented. 

If  the  oxygen  is  withheld  from  the  eggs  immediately  after 
they  become  mature  their  life  is  also  saved.  A.  P.  Mathews 
has  repeated  this  experiment  and  obtained  the  same  results. 
This  proves  that  the  death  of  the  mature  but  unfertilized  egg  is 
determined  by  oxidations.  If  these  oxidations  are  inhibited 
death  does  not  occur.  When  these  experiments  were  first 
published  they  caused  opposition.  This  opposition  was  based 
on  the  fact  that  potassium  cyanide  was  used  in  part  of  the 
experiments.  The  objection  was  raised  that  the  potassium 
cyanide  in  these  experiments  acted  only  by  preventing  the 
development  of  bacteria.  The  authors,  however,  who  raised 
this  objection,  overlooked  the  fact  that  lack  of  oxygen  acts  in 
exactly  the  same  way  as  the  addition  of  potassium  cyanide, 


Peevention  of  Death  by  Fertilization       157 

and  that  it  is  entirely  immaterial  how  lack  of  oxygen  is  pro- 
duced, whether  the  oxygen  is  driven  out  by  carefully  purified 
hydrogen  or  whether  the  eggs  are  put  together  in  a  large  heap, 
whereby  only  those  lying  on  the  surface  of  the  heap  receive 
sufficient  oxygen. 

It  is,  however,  easy  to  show  directly  that  the  above- 
mentioned  objection  is  incorrect.  The  eggs  of  the  star-fish  can 
easily  be  put  into  sterilized  sea-water  without  bacterial  infec- 
tion. The  following  experiment  was  tried.  The  eggs  of  a 
star-fish  were  separated  into  three  parts:  one  part  was  put 
aseptically  into  a  series  of  flasks  with  sterilized  sea- water;  the 
second  part  was  put  into  ordinary  sea-water  without  asepsis; 
the  third  part  was  put  into  sea-water  to  which  a  large  quantity 
of  a  putrid  culture  of  bacteria  had  been  added  that  had 
developed  on  the  dead  eggs  of  the  star-fish.  It  was  found  that 
in  all  three  cases  the  mature  eggs  died  within  the  same  period  of 
time.  The  sterilization  of  the  eggs  of  the  first  group  was 
complete,  as  was  shown  by  the  fact  that  the  eggs  although  dead 
preserved  their  form  for  two  months,  while  the  dead  eggs  in  the 
normal  sea-water  were  completely  destroyed  in  a  few  days  by 
the  action  of  the  bacteria. 

It  is,  therefore,  certain  that  the  death  of  the  star-fish  eggs 
which  are  not  fertilized  is  not  caused  by  bacteria,  but  by  the 
process  of  oxidation  in  the  egg.  If  no  spermatozoon  enters  the 
egg,  or  if  the  egg  is  not  caused  to  develop  by  chemical  treatment 
it  perishes  very  rapidly.  If,  however,  a  spermatozoon  enters 
the  egg,  the  latter  remains  alive  in  spite  of  the  fact  that  the 
entrance  of  the  spermatozoon  causes  an  acceleration  of  the 
oxidations  in  the  egg.  Warburg  found  for  the  eggs  of  the  sea- 
urchin  at  Naples  that  fertilization  raises  the  velocity  of  the 
process  of  oxidations  to  six  times  their  original  value,  while 
Wasteneys  and  I  found  that  fertilization  caused  an  increase 
in  the  velocity  of  oxidations  of  Arhacia  in  Woods  Hole  to  three 
or  four  times  the  rate  found  in  the  unfertilized  eggs. 


158         The   Mechanistic  Conception  of  Life 


How  can  we  explain  the  fact  that  fertilization  saves  the  life 
of  the  egg  ?  Let  us  make  the  following  prelimuiary  assumption : 
The  unfertilized  egg  contains  a  poison,  or  some  faulty  combina- 
tion of  conditions  which,  if  oxidations  take  place,  causes  the 
death  of  the  egg.  In  the  unfertilized  but  mature  egg  oxidations 
take  place.  The  spermatozoon  carries  into  the  egg  among 
other  substances  something  which  protects  the  egg  against  the 
fatal  effects  of  the  oxidations,  and  allows  them  even  to  carry  on 
oxidations  at  an  increased  rate  without  suffering.  We  might 
say  that  the  mature  but  unfertilized  egg  is  comparable  to  an 
anaerobic  being  for  which  oxidations  are  fatal,  and  that  the 
spermatozoon  transforms  the  egg  into  an  aerobic  organism. 

If  we  compare  the  eggs  of  different  animals,  we  j&nd  great 
differences  in  regard  to  the  above-mentioned  conditions.  The 
eggs  of  certain  annelids  (Polynoe)  also  perish  rapidly  if  they 
become  mature  without  being  caused  to  develop,  while  the 
eggs  of  the  sea-urchin  remain  alive  for  a  longer  period  of  time 
after  they  have  become  mature.  The  problem  as  to  what 
determines  this  difference  has  not  yet  been  investigated. 

II 

The  analysis  of  the  process  of  fertilization  by  the  spermato- 
zoon shows  that  we  must  discriminate  between  two  kinds  of 
effects,  the  hereditary  effect  and  the  activating  or  develop- 
mental effect.  The  experiments  on  artificial  parthenogenesis 
make  it  very  probable  that  the  two  groups  of  substances,  the 
substances  which  determine  the  heredity  of  paternal  characters 
and  the  substances  which  cause  the  egg  to  develop,  are  entirely 
different.  In  this  paper  we  are  concerned  only  with  the 
second  group  of  substances,  namely,  those  which  cause  the 
development  of  the  egg. 

The  analysis  of  the  causation  of  development  of  the  egg 
by  a  spermatozoon  has  shown  that  the  latter  acts  by  carrying 
at  least  two  substances  or  groups  of  substances  into  the  egg. 


Prevention  of  Death  by  Fertilization       159 


The  first  of  these  substances  causes  the  formation  of  a  mem- 
brane; the  second  serves  the  purpose  of  rendering  the  egg 
immune  against  the  fatal  action  of  oxidations. 

I  have  shown  in  a  number  of  papers  that  the  essential 
feature  in  the  causation  of  the  development  of  the  egg  is  a 


Fig.  48 


Fig.  49 


Fig.  50 

Figs.  48-50. — Disintegration  of  the  sea-urchin  egg  after  the  membrane  for- 
mation with  butyric  acid,  or  with  foreign  serum  or  with  the  extract  of  sperm  or  of 
foreign  cells;  if  the  eggs  are  not  treated  after  the  membrane  formation  with  a 
hypertonic  solution  or  a  suppression  of  oxidations.  A  indicates  the  area  where 
the  disintegration  begins. 


modification  of  its  surface,  which  in  many  cases  leads  to  the 
formation  of  a  membrane.  If  we  cause  membrane  formation  in 
an  unfertilized  sea-urchin  egg  by  artificial  means,  it  begins  to 
develop,  but  very  soon  perishes;  much  more  rapidly  than 
if  it  is  not  exposed  to  any  treatment.     I  was  able  to  show  that 


160         The   Mechanistic  Conception  of  Life 

this  rapid  death  of  the  sea-urchin  egg,  after  artificial  membrane 
formation,  can  be  prevented  either  by  withdrawing  the  oxygen 
from  the  egg  or  by  inhibiting  the  oxidations  in  the  egg  by  the 
addition  of  a  trace  of  potassium  cyanide.  The  membrane 
formation,  therefore,  causes  the  rapid  death  of  the  egg  through 
an  acceleration  of  oxidations.  Warburg  has  recently  shown 
that  the  artificial  membrane  formation  in  the  unfertilized  sea- 
urchin  egg  causes  the  same  increase  in  the  rapidity  of  oxidations 
as  the  entrance  of  a  spermatozoon. 

If  we  wish  to  cause  the  unfertilized  eggs  to  develop  to  the 
pluteus  stage  after  the  membrane  formation,  we  have  to  subject 
them  to  a  second  treatment.  This  may  consist  in  putting  them 
about  fifteen  minutes  after  the  membrane  formation  into  a 
hypertonic  solution  of  a  certain  osmotic  pressure  (for  instance, 
50  c.c.  of  sea-water+8  c.c.  n/2j  NaCl)  for  one-half  to  one  hour. 
If,  after  this  time,  they  are  put  back  into  normal  sea-water  they 
no  longer  perish,  but  develop  into  normal  larvae.  I  ventured 
the  hypothesis  that  the  artificial  membrane  formation  causes 
a  rapid  increase  of  the  oxidations  in  the  egg  and  in  this  way 
causes  it  to  develop,  but  that  these  oxidations  lead  to  the  rapid 
decay  of  the  eggs  at  room  temperature  for  the  reason  that  the 
egg  contains  a  toxic  substance,  or  a  toxic  complex  of  conditions, 
which  in  the  presence  of  oxidations  leads  to  the  rapid  death  of 
the  egg.  The  second  treatment  serves  the  purpose  of  rendering 
the  egg  immune  against  the  toxic  effects  of  the  oxidations. 

If  we  first  cause  the  artificial  membrane  formation  in  the 
unfertilized  egg  by  any  of  the  various  means  which  I  have 
described  in  former  papers,  and  if  we  afterward  treat  the  eggs 
for  a  short  time  with  a  hypertonic  solution,  they  develop  after 
being  transferred  to  normal  sea-water  in  the  same  way  as  if  a 
spermatozoon  had  entered  them.  They  reach  the  successive 
larval  stages,  develop  into  a  blastula,  gastrula,  and  pluteus,  and 
live  as  long  as  the  larvae  produced  from  eggs  fertilized  by  a 
spermatozoon. 


Prevention  of  Death  by  Fertilization       161 

Hence  the  physico-chemical  activation  of  the  unfertilized 
egg  of  the  sea-urchin  consists  of  two  kinds  of  treatment.  The 
one  is  a  change  in  the  surface  of  the  egg  which  may  or  may 
not  result  in  the  so-called  formation  of  the  membrane.  This 
change  causes  the  acceleration  of  oxidations  which  in  my  opinion 
is  the  essential  feature  of  the  process  of  fertilization.  The 
second  treatment  consists  in  abolishing  the  faulty  condition 
which  makes  oxidations  fatal  to  the  egg.  This  second  treat- 
ment may  consist  in  exposing  the  eggs  for  about  half  an  hour 
or  a  little  more  to  a  hypertonic  solution.  We  can  substitute, 
however,  for  this  treatment  another  treatment,  namely,  the 
deprivation  of  the  egg  for  three  hours  from  oxidations,  either 
by  removing  the  oxygen  from  the  solution  or  by  adding  a  trace 
of  potassimn  cyanide  to  the  solution.  If,  after  the  treatment 
with  the  hypertonic  solution  for  half  an  hour,  or  the  treat- 
ment with  lack  of  oxygen  for  about  three  hours,  the  eggs  are 
put  back  into  normal  sea-water  they  can  develop  into  normal 
larvae. 

We  can  show  that  the  spermatozoon  also  causes  the  develop- 
ment of  the  egg  by  two  different  agencies  comparable  in  their 
action  to  the  agencies  used  in  the  methods  of  chemical  fertiliza- 
tion which  we  have  just  described. 

For  this  purpose  we  must  fertilize  the  egg  of  the  sea-urchin 
with  a  sperm  different  from  its  own,  and  for  the  following 
reason:  The  spermatozoon  of  the  sea-urchin  enters  so  rapidly 
into  the  egg  that  it  is  impossible  to  show  that  it  causes  the 
development  of  the  egg  by  two  different  substances. 

If,  however,  we  fertilize  the  sea-urchin  egg  with  the  sperm 
of  star-fish,  it  takes  from  ten  to  fifty  minutes  to  cause  the 
membrane  formation  in  the  eggs,  the  reason  being  that  the 
star-fish  sperm  can  penetrate  only  very  slowly  into  the  egg  of 
the  sea-urchin. 

It  is,  as  a  rule,  not  possible  to  fertilize  the  egg  of  the  sea- 
urchin  by  star-fish  sperm  in  normal  sea-water.     But  I  found 


162         The   Mechanistic  Conception  of  Life 

eight  years  ago  that  if  we  make  the  sea-water  slightly  more 
alkaline  than  it  naturally  is  the  eggs  of  the  sea-urchin  can  be 
fertilized  by  the  sperm  of  the  star-fish.  For  the  fertilization 
of  the  Californian  sea-urchin,  Strongylocentrotus  purpuratus, 
with  the  sperm  of  Asterias,  the  best  results  were  obtained  when 
0.6  c.c.  of  n/10  NaOH  were  added  to  50  c.c.  of  sea-water.  In 
this  case,  with  active  sperm,  in  about  fifty  minutes  all  the  eggs 
form  the  typical  fertilization  membrane. 

If  we  watch  the  further  development  of  sea-urchin  eggs 
fertilized  by  star-fish  sperm  we  notice  very  soon  that  there  are 
two  different  kinds  of  eggs  present;  the  one  kind  of  eggs 
behave  as  if  they  had  been  fertilized  with  sperm  of  their  own 
kind.  That  is  to  say,  they  segment  regularly  and  develop  into 
swimming  blastulae  and  gastrulae.  The  other  kind  of  eggs, 
however,  act  as  if  they  had  been  treated  with  one  of  the  agencies 
which  cause  the  membrane  formation  in  the  unfertilized  sea- 
urchin  egg;  these  eggs  begin  to  segment,  but  at  room  tempera- 
ture they  slowly  perish  by  cytolysis.  If,  however,  these  eggs 
are  treated  for  half  an  hour  with  a  hypertonic  solution  they 
develop  into  larvae. 

If  we  examine  the  eggs  of  a  sea-urchin  which  have  been 
treated  in  an  alkaline  medium  with  the  sperm  of  the  star-fish, 
we  find  that  only  a  certain  percentage  of  these  eggs  contain 
the  sperm  nucleus,  and  this  percentage  seems  to  be  identical 
with  the  percentage  of  the  eggs  which  develop  into  larvae. 
As  far  as  the  other  eggs  are  concerned,  which  form  only  a 
membrane  and  then  disintegrate,  no  sperm  nucleus  can  be 
found  inside  of  them.  I  am  inclined  to  draw  the  following 
conclusion  from  these  observations:  The  spermatozoon  of  the 
star-fish  penetrates  very  slowly  through  the  surface  film  of 
the  sea-urchin  egg.  When  it  lingers  for  some  time  partially 
imbedded  in  the  surface  film,  one  of  the  substances  of  the 
spermatozoon  is  dissolved  in  the  superficial  layer  of  the  egg 
and   causes  the  membrane   formation.     Through  the  act  of 


Prevention  of  Death  by  Fertilization       163 

membrane  formation  the  further  entrance  of  the  spermatozoon 
into  the  egg  is  prevented,  since  the  fertilization  membrane  is 
impermeable  to  sperm.  This  membrane  formation  leads  to  an 
increase  in  the  rate  of  oxidations  and  the  beginning  of  the  de- 
velopment of  the  egg.  The  latter,  however,  contains  a  toxic 
substance,  or  a  faulty  complex  of  conditions  which  has  to  be 
abolished,  before  the  oxidations  necessary  for  development  can 
take  place  without  the  egg  being  destroyed  by  them.  The 
spermatozoon  carries  a  second  substance  into  the  egg  which 
renders  it  immune  against  the  fatal  actions  of  the  oxidations. 
While  the  membrane-forming  substance  of  the  spermatozoon 
may  be  situated  at  its  surface,  or  superficially  at  least,  the 
second  substance  which  transforms  the  egg  from  an  anaerobe 
into  an  aerobe  must  be  situated  in  the  interior  of  the  sperma- 
tozoon; since  it  can  only  act  if  the  spermatozoon  penetrates 
into  the  egg.  We  see  in  these  observations,  concerning  the 
fertilization  of  the  sea-urchin  egg  by  the  star-fish  sperm,  a 
proof  that  the  activation  of  the  egg  by  the  spermatozoon  is 
also  caused  by  two  different  substances,  one  of  which  causes 
the  membrane  formation,  while  the  second  renders  the  egg 
immune  against  the  toxic  action  of  the  oxidations.  These 
data  support  the  assumption  made  above  that  the  life-saving 
action  of  the  spermatozoon  is  due  to  the  fact  that  it  carries  a 
substance  into  the  egg  which  renders  the  latter  immune  against 
the  toxic  action  of  oxidations. 

Ill 

Seven  years  ago  I  found  that  a  number  of  agencies  destroy 
the  fertilized  egg  much  more  rapidly  than  the  unfertilized  egg- 
Thus,  for  instance,  while  in  a  pure  sodium  chloride  solution  the 
unfertilized  egg  of  the  Californian  sea-urchin  may  be  kept  alive 
for  several  days,  the  fertilized  egg  is  destroyed  in  such  a  solu- 
tion in  less  than  twenty-four  hours.  If  we  use  slightly  alka- 
line solutions  of  sodium  chloride  the  greater  resistance  of  the 


164         The   Mechanistic   Conception  of  Life 

unfertilized  egg  is  perhaps  still  niore  striking.  The  egg  of  the 
Atlantic  form  of  sea-urchin,  Arhada,  is  cytolyzed  in  a  neutral 
sodium  chloride  solution  in  a  few  hours,  while  the  unfertilized  egg 
may  live  for  a  considerably  longer  period  of  time.  When  we 
put  fertilized  and  unfertilized  eggs  into  hypertonic  solutions, 
we  find  also  that  the  fertilized  eggs  suffer  much  more  than  the 
unfertilized.  What  causes  this  difference  of  sensitiveness 
between  fertilized  and  unfertilized  eggs?  It  is  possible  that 
the  permeability  of  the  fertilized  eggs  is  greater  than  that 
of  the  unfertilized.  While  this  is  probably  to  some  extent 
true,  yet  it  is  not  the  whole  explanation  of  the  difference  in  the 
behavior  of  the  two  kinds  of  eggs.  I  have  been  able  to  show  for 
a  number  of  toxic  solutions  that  their  effect  can  be  either  com- 
pletely annihilated  or  at  least  diminished  if  we  take  the  oxygen 
away  from  the  solution.  Thus,  for  instance,  fertilized  eggs  of 
the  sea-urchin  which  perish  very  rapidly  in  pure  salt  solutions, 
or  a  solution  of  sodium + calcium,  or  a  solution  of  sodium + 
barium,  can  be  kept  alive  for  a  considerable  period  of  time  in 
the  same  solutions  if  we  either  carefully  remove  the  oxygen  from 
the  solutions,  or  if  we  diminish  the  rate  of  the  oxidations  in  the 
eggs  by  adding  a  trace  of  sodium  cyanide.  In  this  case  we  have 
the  direct  proof  that  solutions  which  are  fatal  for  the  egg  when 
the  oxidations  are  allowed  to  go  on  are  rendered  completely,  or 
at  least  partially,  harmless  if  we  stop  the  oxidations  in  the  egg. 
Not  only  the  toxic  action  of  salt  solutions  upon  the  fertilized 
egg  could  be  inhibited  by  the  suppression  of  the  oxidations  in  the 
egg,  but  also  the  toxic  action  of  sugar  solutions,  or  of  solutions  of 
alcohol  in  the  sea-water,  or  of  a  solution  of  chloral  hydrate.^ 

These  observations  prove  directly  that  in  the  presence 
of  certain  toxic  substances  or  mixtures  of  substances  the 
oxidations  in  the  egg  lead  to  its  rapid  destruction;  while  a 
suppression  of  the  oxidation  saves  the  life  of  the  egg. 

1  Or  of  phenylurethane.  This  observation  does  not  agree  very  weU  with  the 
assumption  that  the  narcotic  action  of  these  substances  is  due  to  a  retardation  of 
oxidation. 


^^1     Prevention  of  Death  by  Fertilization       165 

We  therefore  believe  that  we  may  conclude  that  the  rapid 
death  of  the  unfertilized  egg  of  certain  species  is  caused  by  the 
oxidations  which  take  place  in  these  eggs;  and  that  the  life- 
saving  action  of  the  spermatozoon  consists  in  the  fact  that  the 
latter,  in  addition  to  the  membrane-forming  substance,  carries 
a  second  substance,  or  group  of  substances,  into  the  egg  which 
renders  it  immune  against  the  harmful  effect  or  consequences 
of  oxidations. 


IX.    THE   ROLE  OF  SALTS  IN  THE  PRESERVATION 

OF  LIFE 


IX 

THE  ROLE  OF  SALTS  IN  THE  PRESERVATION  OF  LIFE^ 

I 

Less  is  known  of  the  role  of  the  salts  in  the  animal  body 
than  of  the  role  of  the  three  other  main  food-stuffs,  namely, 
carbohydrates,  fats,  and  proteins.  As  far  as  the  latter  are  con- 
cerned, we  know  at  least  that  through  oxidation  they  are 
capable  of  furnishing  heat  and  other  forms  of  energy.  The 
neutral  salts,  however,  are  not  oxidizable.  Yet  it  seems  to  be  a 
fact  that  no  animal  can  live  on  an  ash-free  diet  indefinitely, 
although  no  one  can  say  why  this  should  be  so.  We  have  a 
point  of  attack  for  the  investigation  of  the  role  of  the  salts  in 
the  fact  that  the  cells  of  our  body  live  longest  in  a  liquid  which 
contains  the  three  salts,  NaCl,  KCl,  and  CaCla  in  a  definite 
proportion,  namely,  100  molecules  NaCl,  2.2  molecules  KCl, 
and  1 . 5  molecules  of  CaClg.  This  proportion  is  identical  with 
the  proportion  in  which  these  salts  are  contained  in  sea-water; 
but  the  concentration  of  the  three  salts  is  not  the  same  in  both 
cases.  It  is  about  three  times  as  high  in  the  sea-water  as  in  our 
blood  serum. 

Biologists  have  long  been  aware  of  the  fact  that  the  ocean 
has  an  incomparably  richer  fauna  than  fresh-water  lakes  or 
streams  and  it  is  often  assumed  that  life  on  our  planet  originated 
in  the  ocean.  The  fact  that  the  salts  of  Na,  Ca,  and  K  exist  in 
about  the  same  proportion  in  our  blood  serum  as  in  the  ocean 
has  led  some  authors  to  the  conclusion  that  our  ancestors  were 
marine  animals,  and  that,  as  a  kind  of  inheritance,  we  still  carry 
diluted  sea-water  in  our  blood.     Statements  of  this  kind  have 

1  Carpenter  lecture  delivered  at  the  Academy  of  Medicine  of  New  York, 
October  19,  1911.  Reprinted  from  Science,  N.S.,  XXXIV,  No.  881,  653-65, 
November  17,  1911,  by  courtesy  of  Professor  James  McKeen  Cattell. 

169 


170         The  Mechanistic  Conception  of  Life 

mainly  a  metaphorical  value,  but  they  serve  to  emphasize  the 
two  facts,  that  the  three  salts,  NaCl,  KCl,  and  CaClg,  exist  in 
our  blood  in  the  same  relative  proportion  as  in  the  ocean  and  that 
they  seem  to  play  an  important  role  in  the  maintenance  of  life. 
I  intend  to  put  before  you  a  series  of  experiments  which 
seem  to  throw  some  light  on  the  mechanism  by  which  the 
solutions  surrounding  living  cells  influence  their  duration  of  life. 

II 

In  order  to  give  a  picture  of  the  extent  to  which  the  life  of 
many  animals  depends  upon  the  cooperation  of  the  three  salts  I 
may  mention  experiments  made  on  a  small  marine  crustacean, 
Gammarus,  of  the  Bay  of  San  Francisco.  If  these  animals  are 
suddenly  thrown  into  distilled  water,  their  respiration  stops 
(at  a  temperature  of  20°  C.)  in  about  half  an  hour.  If  they  are 
put  back  immediately  after  the  cessation  of  respiration  into 
sea-water,  they  can  recuperate.  If  ten  minutes  or  more  are 
allowed  to  elapse  before  bringing  them  back  into  the  sea-water, 
no  recuperation  is  possible.  Since  in  this  case  death  is  caused 
obviously  through  the  entrance  of  distilled  water  into  the 
tissues  of  the  animals,  one  would  expect  that  the  deadly  effect 
of  distilled  water  would  be  inhibited  if  enough  cane  sugar  were 
added  to  the  distilled  water  to  make  the  osmotic  pressure  of 
the  solution  equal  to  that  of  the  sea-water.  If,  however,  the 
animals  are  put  into  cane-sugar  solution,  the  osmotic  pressure 
of  which  is  equal  to  that  of  sea- water,  the  animals  die  just 
about  as  rapidly  as  in  distilled  water.  The  same  is  true  if  the 
osmotic  pressure  of  the  sugar  solution  is  higher  or  lower  than 
that  of  the  sea-water.  The  sugar  solution  is,  therefore,  about 
as  toxic  for  these  animals  as  the  distilled  water,  although  in  the 
latter  case  water  enters  into  the  tissues  of  the  animal,  while 
in  the  former  case  it  does  not. 

If  the  sea-water  is  diluted  with  an  equal  quantity  of  distilled 
water  in  one  case,  and  of  isotonic  cane-sugar  solution  in  the 


Role  of  Salts  in  Preservation  of  Life      171 

other,  in  both  cases  the  duration  of  life  is  shortened  by  practi- 
cally the  same  amount. 

If  the  crustaceans  are  brought  into  a  pure  solution  of  NaCl, 
of  the  same  osmotic  pressure  as  the  sea-water,  they  also  die  in 
about  half  an  hour.  If  to  this  solution  a  little  calcium  chloride 
be  added  in  the  proportion  in  which  it  is  contained  in  the  sea- 
water  the  animals  die  as  rapidly  as  without  it.  If,  however, 
both  CaCl2  and  KCl  are  added  to  the  sodium  chloride  solution, 
the  animals  can  live  for  several  days.  The  addition  of  KCl 
alone  to  the  NaCl  prolongs  their  life  but  little. 

If  KCl  and  CaCl2  are  added  to  a  cane-sugar  solution  isotonic 
with  sea-water,  the  animals  die  as  quickly  or  more  so  than  in  the 
pure  cane-sugar  solution. 

If  other  salts  be  substituted  for  the  three  salts  the  animals 
die.  The  only  substitution  possible  is  that  of  SrClg  for  CaCla- 
We  find  also  that  the  proportion  in  which  the  three  salts  of 
sodium,  calcium,  and  potassium  have  to  exist  in  the  solution 
cannot  be  altered  to  any  extent.  All  this  leads  us  to  the  con- 
clusion, that  in  order  to  preserve  the  life  of  the  crustacean 
Gammarus,  the  solution  must  not  only  have  a  definite  concentra- 
tion or  osmotic  pressure  but  that  this  osmotic  pressure  must  be 
furnished  by  definite  salts,  namely,  sodium  chloride,  calcium 
chloride,  and  potassium  chloride  in  the  proportion  in  which 
these  three  salts  exist  in  the  sea-water  (and  in  the  blood) ;  this 
fact  could  also  be  demonstrated  for  many  other  marine  animals. 
The  relative  tolerance  of  various  cells  and  animals  for  abnormal 
salt  solutions  is,  however,  not  the  same,  a  point  which  we  shall 
discuss  later  on. 

Ill 

What  is  the  role  of  the  salts  in  these  cases  ?  The  botanists 
have  always  considered  salt  solutions  as  nutritive  solutions. 
It  is  a  well-known  fact  that  plants  require  definite  salts,  e.g., 
nitrates  and  potassium  salts,  for  their  nutrition,  and  the  ques- 
tion now  arises  whether  the  three  salts  NaCl,  KCl,  and  CaCla, 


172         The  Mechanistic  Conception  of  Life 

which  are  needed  for  the  preservation  of  animal  life,  play  the 
role  of  nutritive  salts.  Experiments  which  I  made  on  a  small 
marine  fish,  Fundulus,  proved  beyond  question  that  this  is  not 
the  case.  If  the  young,  newly  hatched  fish  are  put  into  a  pure 
solution  of  sodium  chloride  of  the  concentration  in  which  this 
salt  is  contained  in  sea-water,  the  animals  very  soon  die.  If, 
however,  KCl  and  CaClg  be  added  to  the  solution  in  the  right 
proportion,  the  animals  can  live  indefinitely.  These  fish, 
therefore,  behave  in  this  respect  like  Gammarus  and  the  tissues 
of  the  higher  animals,  but  they  differ  from  Gammarus  and  the 
majority  of  marine  animals  inasmuch  as  the  fish  can  live  long, 
and  in  some  cases,  indefinitely,  in  distilled  and  fresh  water, 
and  certainly  in  a  very  dilute  solution  of  sodium  chloride. 
From  this  fact  I  drew  the  conclusion  that  KCl  and  CaClg  do  not 
act  as  nutritive  substances  for  these  animals,  that  they  only 
serve  to  render  NaCl  harmless  if  the  concentration  of  the  latter 
salt  is  too  high.  I  succeeded  in  showing  that  as  long  as  the 
sodium  chloride  solution  is  very  dilute  and  does  not  exceed  the 
concentration  of  m/8,  the  addition  of  KCl  and  CaClg  is  not 
required.  Only  when  the  solution  of  NaCl  has  a  concentration 
above  m/8  does  it  become  harmful  and  require  the  addition  of 
KCl  and  CaCl^. 

The  experiments  on  Fwndttto,  therefore,  prove  that  a  mixture 
of  NaCl + KCl  H-CaClg  does  not  act  as  a  nutritive  solution,  but 
as  a  protective  solution.  KCl  and  CaCla  are  only  necessary  in 
order  to  prevent  the  harmful  effects  which  NaCl  produces  if 
it  is  alone  in  solution  and  if  its  concentration  is  too  high.  We 
are  dealing,  in  other  words,  with  a  case  of  antagonistic  salt 
action;  an  antagonism  between  NaCl  on  the  one  hand  and  KCl 
and  CaClg  on  the  other.  The  discovery  of  antagonistic  salt 
action  was  made  by  Ringer,  who  found  that  there  is  a  certain 
antagonism  between  K  and  Ca  in  their  action  on  the  heart. 
When  he  put  the  heart  of  a  frog  into  a  mixture  of  NaCl + KCl 
he  found  that  the  contractions  of  the  heart  were  not  normal, 


Role  of  Salts  in  Preservation  of  Life       173 

but  they  were  rendered  normal  by  the  addition  of  a  Httle  CaClg. 
A  mixture  of  NaCl+CaClg  also  caused  abnormal  contractions 
of  the  heart,  but  these  were  rendered  normal  by  the  addition 
of  KCl.  Ringer  drew  the  conclusion  that  there  existed  an 
antagonism  between  potassium  and  calcium,  similar  to  that 
which  Schmiedeberg  had  found  between  different  heart  poisons, 
e.g.,  atropin  and  muscarin.  Biedermann  had  found  that  alka- 
line salt  solutions  cause  twitchings  in  the  muscle  and  Ringer 
found  that  the  addition  of  Ga  inhibited  these  twitchings. 
Since  these  experiments  were  made  many  examples  of  the 
antagonistic  action  of  salts  have  become  known. 

It  had  generally  been  assumed  that  the  antagonistic  action 
of  two  salts  was  based  on  the  fact  that  each  salt,  when  applied 
singly,  acted  in  the  opposite  way  from  that  of  its  antagonist. 
We  shall  see  that  in  certain  cases  of  antagonistic  salt  action  at 
least  this  view  is  not  supported  by  fact. 

IV 

What  is  the  mechanism  of  antagonistic  salt  action?  I 
believe  that  an  answer  to  this  question  lies  in  the  follo^TQg 
observations  on  the  eggs  of  Fundulus.  If  these  eggs  are  put 
immediately  after  fertilization  into  a  pure  sodium  chloride 
solution  which  is  isotonic  with  sea-water,  they  usually  die 
without  forming  an  embryo.  If,  however,  only  a  trace  of  a 
calcium  salt,  or  of  any  other  salt  with  a  bivalent  metal  (with 
the  exception  of  Hg,  Cu,  or  Ag)  is  added  to  the  m/2  NaCl 
solution,  the  toxicity  of  the  solution  is  diminished  or  even 
abolished.  Even  salts  which  are  very  poisonous,  namely,  salts 
of  Ba,  Zn,  Pb,  Ko,  Ni,  Mn,  and  other  bivalent  metals,  are  able 
to  render  the  pure  solution  of  sodium  chloride  harmless,  at 
least  to  the  extent  that  the  eggs  can  live  long  enough  to  form 
an  embryo.  The  fact  that  a  substance  as  poisonous  as  Zn  or 
lead  can  render  harmless  a  substance  as  indifferent  as  sodium 
chloride  seems  so  paradoxical  that  it  demanded  an  explanation, 


174         The  Mechanistic  Conception  of  Life 

and  this  explanation  casts  light  on  the  nature  of  the  protective 
or  antagonistic  action  of  salts.  For  the  antagonistic  action  of 
a  salt  of  lead  or  zinc  against  the  toxic  action  of  sodium  chloride 
can  only  consist  in  the  lead  salt  protecting  the  embryo  against 
the  toxic  action  of  the  NaCl.  But  how  is  this  protective 
action  possible  ? 

We  have  mentioned  that  if  we  put  the  young  fish,  imme- 
diately after  hatching,  into  a  pure  m/2  solution  of  sodium 
chloride  the  animals  die  very  quickly,  but  that  they  live 
indefinitely  in  the  sodium  chloride  solution  if  we  add  both 
CaClg  and  KCl.  How  does  it  happen  that  for  the  embryo,  as 
long  as  it  is  in  the  egg  shell,  the  addition  of  CaClg  to  the  NaCl 
solution  suffices,  while  if  the  fish  is  out  of  the  shell  the  addition 
of  CaCl2  alone  is  no  longer  sufficient  and  the  addition  of  KCl 
also  becomes  necessary  ?  Moreover,  if  we  try  to  preserve  the 
life  of  the  fish  after  it  is  taken  out  of  the  egg  in  an  m/2  sodium 
chloride  solution  by  adding  ZnSO^,  or  lead  acetate,  to  the  solu- 
tion we  find  that  the  fish  die  even  much  more  quickly  than 
without  the  addition.^ 

If  we  look  for  the  cause  of  this  difference  our  attention 
is  called  to  the  fact  that  the  fish,  as  long  as  it  is  in  the  egg,  is 
separated  from  the  surrounding  solution  by  the  egg  membrane. 
This  egg  membrane  possesses  a  small  opening,  the  so-called 
micropyle,  through  which  the  spermatozoon  enters  into  the  egg. 
I  have  gained  the  impression  that  this  micropyle  is  not  closed 
as  tightly  immediately  after  fertilization  as  later  on,  since  the 
newly  fertilized  egg  is  killed  more  rapidly  by  an  m/2  solution  of 
NaCl  than  it  is  killed  by  the  same  solution  one  or  two  days 
after  fertilization.  One  can  imagine  that  the  micropyle  con- 
tains a  wad  of  a  colloidal  substance  which  is  hardened  gradually 
to  a  leathery  consistency  if  the  egg  remains  in  the  sea-water. 

1  R.  LiUie  has  found  that  in  the  larvae  of  Arenicola  a  slight  antagonism 
between  NaCl  and  ZnS04  can  be  proved.  This  shows  that  the  general  laws  of 
antagonism  between  two  salts  differ  in  degree  but  not  in  principle  in  the  living 
organism  and  the  dead  envelop  of  the  fish  egg. 


Role  of  Salts  in  Preservation  of  Life      175 

With  the  process  of  hardening,  or  tanning,  it  becomes  more 
impermeable  for  the  NaCl  solution.  This  process  of  hardening 
is  brought  about  apparently  very  rapidly  if  we  add  to  the  m/2 
NaCl  solution  a  trace  of  a  salt  of  a  bivalent  metal  like  Ca,  Sr, 
Ba,  Zn,  Pb,  Mn,  Ko,  and  Ni,  etc.  It  is  also  possible  that  similar 
changes  take  place  in  the  whole  membrane.  The  process  of 
rendering  the  m/2  Na  solution  harmless  for  the  embryo  of  the 
fish,  therefore,  depends  apparently  upon  the  fact  that  the  addi- 
tion of  the  bivalent  metals  renders  the  micropyle  or  perhaps 
the  whole  membrane  of  the  egg  more  impermeable  to  NaCl 
than  was  the  case  before. 

But  these  are  only  one  part  of  the  facts  which  throw  a  light 
upon  the  protective  or  antagonistic  action  of  salts.  Further 
data  are  furnished  by  experiments  which  I  made  together  with 
Professor  Gies,  also  on  the  eggs  of  Fundulus.  Gies  and  I  were 
able  to  show  that  not  only  are  the  bivalent  metals  able  to  render 
the  sodium  chloride  solution  harmless,  but  that  the  reverse  is 
also  the  case,  namely,  that  NaCl  is  required  to  render  the  solu- 
tions of  many  of  the  bivalent  metals,  for  instance  ZnSO^,  harm- 
less. (That  the  SO^  ion  has  nothing  to  do  with  the  result  was 
shown  before  by  experiments  with  NagSO^.) 

If  the  eggs  of  Fundulus  are  put  immediately  after  fertiliza- 
tion into  distilled  water,  a  large  percentage  of  the  eggs  develop, 
often  as  many  as  100  per  cent,  and  the  larvae  and  embryos 
formed  in  the  distilled  water  are  able  to  hatch.  If  we  add, 
however,  to  100  c.c.  of  distilled  water  that  quantity  of  ZnSO^ 
which  is  required  to  render  the  NaCl  solution  harmless,  all  the 
eggs  are  killed  rapidly  and  not  a  single  one  is  able  to  form  an 
embryo.  If  we  add  varying  amounts  of  NaCl  we  find  that, 
beginning  with  a  certain  concentration  of  NaCl,  this  salt 
inhibits  the  toxic  effects  of  ZnSO^  and  many  eggs  are  able  to 
form  an  embryo.  This  can  be  illustrated  by  the  following 
table : 


176         The   Mechanistic  Conception  of  Life 

TABLE  I 

Percentage  of 
Nature  of  the  Solution  the  Eggs  Forming 

an  Embryo 

100  c.c.  distilled  water 49 

100  c.c.  distilled  water+8  c.c.  m/32  ZnSOi 0 

100  c.c.  m/64  NaCl+8  c.c.  m/32  ZnSO^ 0 

100  c.c.  m/32  NaCl+8  c.c.  m/32  ZnSOi 3 

100  c.c.  m/16  NaCl+S  c.c.  m/32  ZnSO, 8 

100  c.c.  m/8    NaCl+8  c.c.  m/32  ZnSOi 44 

100  c.c.  m/4    NaCl+8  c.c.  m/32  ZnSOi 38 

100  c.c.   3/8    NaCl+8  c.c.  m/32  ZnS04 37 

100  c.c.  m/2    NaCl-f  8  c.c.  m/32  ZnSOi 34 

100  c.c.   5/8    NaCH-8  c.c.  m/32  ZnSO* 29 

100  c.c.   6/8    NaCl+8  c.c.  m/32  ZnSOi 8 

100  c.c.   7/8    NaCl+8  c.c.  m/32  ZnS04 6 

100  c.c.  m       NaCl+8  c.c.  m/32  ZnSO, 1 

This  table  shows  that  the  addition  of  NaCl,  if  its  concentra- 
tion exceeds  a  certain  limit,  namely,  m/8,  is  able  to  render  the 
ZnSO^  in  the  solution  comparatively  harmless. 

If  we  now  assume  that  ZnSO^  renders  the  5/8  m  NaCl  solu- 
tion harmless  by  rendering  the  egg  membrane  comparatively 
impermeable  for  NaCl  we  must  also  draw  the  opposite  conclu- 
sion, namely,  that  NaCl  renders  the  egg  membrane  compara- 
tively impermeable  for  ZnSO^.  We  therefore  arrive  at  a  new 
conception  of  the  mutual  antagonism  of  two  salts,  namely, 
that  this  antagonism  depends,  in  this  case  at  least,  upon  a 
common,  cooperative  action  of  both  salts  on  the  egg  membrane, 
by  which  action  this  membrane  becomes  completely  or  com- 
paratively impermeable  for  both  salts.  And  from  this  we  must 
draw  the  further  conclusion  that  the  fact  that  each  of  these 
salts,  if  it  is  alone  in  the  solution,  is  toxic,  is  due  to  its  com- 
paratively rapid  diffusion  through  the  membrane,  so  that  it 
comes  into  direct  contact  with  the  protoplasm  of  the  germ. 

As  long  as  we  assumed  that  each  of  the  two  antagonistic 
salts  acted,  if  applied  singly,  in  the  opposite  way  from  its 
antagonist,  it  was  impossible  to  understand  these  experiments 


Role  of  Salts  in  Preservation  of  Life      177 

or  find  an  analogue  for  them  in  colloid  chemistry.  But  if  we 
realize  that  NaCl  alone  is  toxic  because  it  is  not  able  to  render 
the  egg  membrane  impermeable;  and  that  ZnSO^  if  alone  in 
solution  is  toxic  for  the  same  reason;  while  both  combined  are 
harmless  (since  for  the  ''tanning"  of  the  membrane  the  action 
of  the  two  salts  is  required)  these  experiments  become  clear. 

We  may,  for  the  sake  of  completeness,  still  mention  that 
salts  alone  have  such  antagonistic  effects;  glycerin,  urea,  and 
alcohol  have  no  such  action.  On  the  other  hand,  ZnSO^  was 
not  only  able  to  render  NaCl  harmless,  but  also  LiCl,  NH^Cl, 
CaClg,  and  others;  and  vice  versa. 

These  experiments  on  the  egg  of  Fundulus  are  theoretically 
of  importance,  since  they  leave  no  doubt  that  in  this  case  at 
least  the  ''antagonistic"  action  of  salts  consists  in  a  modification 
of  the  egg  membrane  by  a  combined  action  of  two  salts,  whereby 
the  membrane  becomes  less  permeable  for  both  salts. 

V 

It  is  not  easy  to  find  examples  of  experiments  in  the  litera- 
ture which  are  equally  unequivocal  in  regard  to  the  character 
of  antagonistic  salt  action;  but  I  think  that  some  recent  experi- 
ments by  Osterhout  satisfy  this  demand. 

It  has  long  been  a  question  whether  or  not  cells  are  at  all 
permeable  for  salts.  Nobody  denies  that  salts  diffuse  much 
more  slowly  into  the  cells  than  water;  but  some  authors, 
especially  Overton  and  Hoeber,  deny  categorically  that  they 
can  diffuse  at  all  into  the  cells.  Overton's  view  is  based  partly 
on  experiments  on  plasmolysis  in  the  cells  of  plants.  If  the 
cells  of  plants,  for  example,  those  of  Spirogyra,  are  put  into  a 
solution  of  NaCl  or  some  other  salt  of  sufficiently  high  osmotic 
pressure,  the  volume  of  the  contents  of  the  cell  decreases 
through  loss  of  water  and  the  protoplasm  retracts,  especially 
from  corners  of  the  rigid  cellulose  walls.  Overton  maintains 
that  this  plasmolysis  is  permanent,  and  concludes  from  this 


178         The  Mechanistic  Conception  of  Life 

that  only  water  but  no  salt  can  diffuse  through  the  cell-wall; 
since  otherwise  salt  should  gradually  diffuse  from  the  solution 
into  the  cell,  and  through  this  increase  in  the  osmotic  pressure 
of  the  cell  the  water  should  finally  diffuse  back  into  the  cell  and 
restitute  the  normal  volume  of  the  cell.  According  to  Overton 
this  does  not  happen. 

Osterhout  has  recently  shown  that  Overton's  observations 
were  incomplete  in  a  very  essential  point  and  that  in  reality 
the  plasmolysis,  which  occurs  in  this  case  when  the  cell  is  put 
into  the  hypertonic  solution,  disappears  again  in  a  time  which 
varies  with  the  nature  of  the  salt  in  solution.  This  stage  of 
reversion  of  plasmolysis  had  been  overlooked  by  Overton.  If 
the  cell,  however,  remains  permanently  in  the  hypertonic 
sodium  chloride  solution,  a  shrinking  of  the  contents  of  the 
cell  takes  place  again,  which  superficially  resembles  plasmolysis, 
but  which  in  reality  has  nothing  to  do  with  plasmolysis,  but 
is  a  phenomenon  of  death.  That  this  second  ''false  plas- 
molysis," as  Osterhout  calls  it,  has  nothing  to  do  with  the  hyper- 
tonic character  of  the  solution  was  proved  by  the  fact  that 
hypotonic  solutions  of  toxic  substances  may  produce  the  same 
phenomenon. 

In  one  experiment  which  Osterhout  describes, 

a  portion  of  a  Spirogyra  filament  was  plasmolyzed  in  .2  m  CaCl2, 
but  not  in  .  195  m  CaCl2.  A  .29  m  NaCl  solution  has  approximately 
the  same  osmotic  pressure  as  a  .2m  CaCl2  solution.  But  on  placing 
another  portion  of  the  same  Spirogyra  filament  in  a  .  29  m  NaCl  solu- 
tion the  expected  plasmolysis  does  not  occur  and  it  is  impossible  to 
plasmolyze  the  cells  until  they  are  placed  in  .  4  m  NaCl. 

Osterhout  explains  this  difference  in  the  concentration  of  the 
two  salts  required  for  plasmolysis  by  the  assumption  that  NaCl 
diffuses  more  rapidly  into  the  cell  than  CaClg,  a  conclusion  which 
I  reached  also  on  the  basis  of  my  earlier  experiments  on  animals. 
Osterhout's  experiments  also  show  that  the  antagonism  of 
NaCl  and  CslCI^  depends  partly  on  the  facts  that  the  two  salts 


Role  of  Salts  in  Preservation  of  Life       179 

inhibit  each  other  from  diffusing  into  the  cells,  and  this  conclu- 
sion is  based  among  others  upon  the  following  experiment. 

By  dividing  a  Spirogyra  filament  into  several  portions  it  was  found 
that  it  was  plasmolyzed  in  .  2  m  CaClg  and  in  .  38  m  NaCl,  but  neither 
in  .195  m  CaCl2  nor  in  .375  m  NaCl.  On  mixing  100  c.c.  .375  m 
NaCl  with  10  c.c.  .  195  m  CaCl2  and  placing  other  portions  of  the  same 
filament  in  it,  prompt  and  very  marked  plasmolysis  occurred. 

The  explanation  for  this  observation  lies  in  the  fact  that  in 
the  mixture  of  NaCl  and  CaClg  the  two  salts  render  their 
diffusion  into  the  cell  mutually  more  difficult.  After  a  longer 
period  of  time  the  plasmolyzed  cells  can  expand  again  in  a 
mixture  of  NaCl  and  CaClg,  but  that  occurs  much  later  than  if 
they  are  in  the  pure  NaCl  solution. 

These  experiments  are  the  analogue  of  the  observation  on  the 
embryo  of  the  eggs  of  Fundulus  in  which  a  pure  solution  of 
ZnSO^  diffused  rapidly  through  the  membrane  or  micropyle, 
while,  if  both  salts  were  present,  the  diffusion  was  inhibited 
or  considerably  retarded. 

While  the  observations  of  Osterhout  show  that  Overton  was 
riot  justified  in  using  the  experiments  on  plasmolysis  to  prove 
that  the  neutral  salts  cannot  diffuse  into  the  cells,  yet  they  do 
not  prove  that  these  salts  diffuse  into  the  cell  under  normal  con- 
ditions. In  Osterhout's  experiments  the  cells  are  in  strongly 
hypertonic  solutions  and  it  does  not  follow  that  such  solutions 
act  like  isotonic,  perfectly  balanced  solutions. 

VI 

Wasteneys  and  I  have  recently  shown  that  the  toxic  action 
of  acids  upon  Fundulus  can  be  annihilated  by  salts.  If  we 
add  0 . 5  c.c.  n/10  butyric  acid  to  100  c.c.  of  distilled  water  these 
fish  die  in  2J  hours  or  less.  In  solutions  which  contain  0.4  c.c. 
or  less  acid  they  can  live  for  a  week  or  more.  If  we  add, 
however,  0.5  c.c.  of  butyric  acid  to  100  c.c.  of  solutions  of  NaCl 
of  various  concentration,  we   find  that  above  a  certain  limit 


180 


The   Mechanistic  Conception  of  Life 


the  NaCl  can  render  the  acid  harmless.  It  is  needless  to 
say  that  the  NaCl  used  in  these  experiments  was  strictly 
neutral  and  that  the  amount  of  acid  present  in  the  mixture  of 
acid  and  salt  was  measured.  The  folio  whig  experiment  may 
serve  as  an  example.  Six  fish  were  put  into  500  c.c.  of  each 
of  the  following  seven  mixtures,  namely, 

1)  100  c.c.  H2O  +0.5  c.c.  n/10  butyric  acid 

2)  96  c.c.  H2O+  4  c.c.  ni/2  NaCl+0.5  c.c.  n/10  butyric  acid 

3)  94  c.c.  H2O+  6  c.c.  ni/2  NaCl+0.5  c.c.  n/10  butyric  acid 

4)  92  c.c.  H2O+  8  c.c.  m/2  NaC14-0.5  c.c.  n/10  butyric  acid 

5)  90  c.c.  H2O+IO  c.c.  m/2  NaCl+0.5  c.c.  n/10  butyric  acid 

6)  88  c.c.  H2O+ 12  c.c.  m/2  NaCl+0. 5  c.c.  n/10  butyric  acid 

7)  85  c.c.  H2O+I5  c.c.  m/2  NaCl+0.5  c.c.  n/10  butyric  acid 

After  certain  intervals  the  number  of  surviving  fish  was 
ascertained.     The  result  is  given  in  Table  II. 


TABLE  II 


Number  of  Surviving  Fish  in  0. 5  c.c.  n/10  Butyric  Acid 

After 

+0 

4.0 

6.0 

8.0 

10.0 

12.0 

15.0 

c.c.  m/2  NaCl  in  100  c.c.  of  the  Solution 

2  hours 

4  hours 

1  day 

2  days 

3  days 

4  days 

0 

0 

0 

2 

0 

.  . 

3 
3 
1 
1 
1 
1 

3 
2 
1 
0 

6 
5 
5 
5 
5 
5 

If  the  amount  of  acid  was  increased,  the  amount  of  NaCl 
also  had  to  be  increased  to  render  the  acid  harmless.  In  order 
to  render  0.5  c.c.  n/10  butyric  acid  pro  100  c.c.  solution  harm- 
less, 10  c.c.  m/2  NaCl  had  to  be  added;  while  0.8  c.c.  butyric 
acid  required  20  c.c.  and  1.0  c.c.  butyric  acid  required  about 
28  c.c.  m/2  NaCl  in  100  c.c.  of  the  solution. 

Not  only  butyric  acid,  but  any  kind  of  acid,  could  be 
rendered  harmless  by  neutral  salts,  e.g.,  HCl  by  NaCl. 


Role  of  Salts  in  Preservation  of  Life       181 

Wasteneys  and  I  could  show  that  the  rate  of  the  absorption 
of  acid  by  the  fish  is  the  same  in  solutions  with  and  without  salt. 
This  proves  that  the  action  of  the  salts  consisted  in  this  case 
not  in  preventing  the  diffusion  or  absorption  of  the  acid,  but  in 
modifying  the  deleterious  effect  of  the  absorbed  acid. 

We  can  state  a  little  more  definitely  the  cause  of  death  by 
acid.  If  we  put  the  fish  into  a  weak  acid  solution  in  distilled 
water  just  strong  enough  to  kill  the  fish  in  from  one  to  two  hours 
(e.g.,  500  c.c.  H2O+2.O  c.c.  n/10  HCl),  we  notice  that  the  acid 
very  soon  makes  the  normally  transparent  epidermis  of  the 
fish  opaque,  and  a  little  later  the  epidermis  falls  off  in  pieces 
and  shreds.  This,  however,  is  probably  not  the  direct  cause 
of  the  death,  but  I  am  inclined  to  assume  that  the  fish  die 
from  suffocation  caused  by  a  similar  action  of  the  acid  upon 
the  gills. 

The  action  of  the  acid  upon  the  epidermis  of  the  body  as 
well  as  upon  the  gills  is  prevented  through  the  addition  of 
neutral  salts. 

.  It  is  well  known  that  the  action  of  acids  upon  proteins  can 
be  inhibited  by  neutral  salts. ^  Thus  the  internal  friction  of 
certain  protein  solutions  is  increased  by  acids  while  the  addition 
of  neutral  salts  inhibits  this  effect  (Pauli).  The  swelling  of 
gelatin  caused  by  acid  is  inhibited  by  salts  (Procter). ^ 

It  is  possible  that  in  the  experiments  with  acid  the  fish  is 
killed  in  the  following  way.  The  acid  causes  certain  proteins 
in  the  surface  layer  of  the  epithelial  cells  of  the  gills  and  of  the 
skin  to  swell,  whereby  this  surface  layer  becomes  more  perme- 
able for  the  acid.  The  acid  can  now  diffuse  into  the  epithelial 
cells  and  act  on  the  protoplasm,  whereby  the  cells  are  killed. 
If  salts  are  present  in  the  right  concentration,  the  combined 
action  of  acid  and  salt  causes  a  dehydration  of  the  surface  film 

1  It  seems  that  the  first  experiments  on  the  antagonism  between  acids  and 
salts  were  published  by  the  author  in  Pfliigers  Archiv,  Vol.  LXXV,  p.  308,  1899. 

2  The  beautiful  osmometric  experiments  of  R.  Lillie  should  also  be  mentioned 
in  this  connection. 


182         The  Mechanistic  Conception  of  Life 

of  these  cells,  as  it  does  in  the  experiments  on  gelatin  or  as  in 
the  cases  of  tanning  of  hides  by  the  combined  action  of  acids 
and  salt  solutions.  This  combined  dehydrating  or  'banning" 
action  of  acid  and  salts  on  the  surface  of  the  epithelial  cells  of  the 
gills  diminishes  the  permeability  of  this  layer  for  the  acids  and 
prevents  them  from  diffusing  into  the  cells  and  thus  destroying 
the  protoplasm.  In  this  way  the  gills  are  kept  intact  and  the 
life  of  the  fish  is  saved. 

As  long  as  the  amount  of  acid  is  small  the  amount  absorbed 
is  not  essentially  diminished  by  the  presence  of  salts ;  but  while 
in  the  presence  of  salts  the  acid  is  consumed  in  the  tanning 
action  of  the  surface  layer  of  the  cells,  or  is  absorbed  in  this 
layer;  if  no  salt  is  present  part  of  the  acid  diffuses  into  the 
epithelial  cells  and  kills  the  latter. 

VII 

We  have  thus  far  considered  the  cases  of  antagonism  between 
two  electrolytes  only.  The  case  of  the  antagonism  between  three 
electrolytes  is  a  little  more  complicated. 

We  choose  as  an  example  the  antagonism  between  NaCl, 
KCl,  and  CaCla — the  antagonism  which  is  most  important  in 
life  phenomena.  If  the  mechanism  of  the  antagonism  between 
NaCl,  on  the  one  hand,  and  KCl  and  CaCl2,  on  the  other,  is  of 
the  same  nature  as  that  between  NaCl  and  ZnSO^  in  the  case  of 
the  eggs  of  Fundulus,  it  must  be  possible  to  show  that  not  only 
is  NaCl  toxic  if  it  is  alone  in  solution,  and  that  it  is  rendered 
harmless  by  the  two  other  salts,  but  that  the  reverse  is  true 
also.  This  can  be  proved  in  the  case  of  KCl.  To  demonstrate 
it,  we  have  again  to  experiment  on  organisms  which  are,  in  wide 
limits,  independent  of  the  osmotic  pressure  of  the  surrounding 
solution  since  the  concentration  of  the  KCl  in  sea-water  is  very 
low.  The  experiments  were  carried  out  by  Mr.  Wasteneys 
and  myself  on  Fundulus.  The  method  consisted  in  putting  six 
fish,  after  washing  them  twice  with  distilled  water,  into  500  c.c. 


Role  of  Salts  in  Preseevation  of  Life      183 

of  the  solution.  It  was  ascertained  from  day  to  day  how  many 
fish  survived. 

When  the  fish  were  put  into  pure  solutions  of  KCl  of  the 
concentration  in  which  this  salt  is  contained  in  the  sea-water 
(2 . 2  c.c.  m/2  KCl  in  100  c.c.  of  the  solution)  they  died  mostly 
in  Idss  than  two  days.  This  is  not  due  to  the  low  concentration 
of  the  KCl  solution,  which  is  only  1/50  of  that  of  the  sea-water, 
since  the  fish  can  live  indefinitely  in  a  pure  NaCl  solution  of  the 
same  concentration  as  that  in  which  the  KCl  exists  in  the  sea- 
water. 

If  we  add  to  the  toxic  quantities  of  KCl  increasing  quantities 
of  NaCl,  we  find  that  as  soon  as  the  solution  contains  17  or  more 
molecules  of  NaCl  to  one  molecule  of  KCl,  the  toxic  action  of 
KCl  is  considerably  diminished,  if  not  completely  counteracted. 
The  following  table  may  serve  as  an  example : 


TABLE  III 


After  Days 

Number  of  Surviving  Fish  in  2.2  c. 

c.  m/2  KCl  IN  100  c.c. 

H.O 

m/lOO 

m/20 

m/8 

m/4 

3  m/8 

m/2 

NaCl 

1 

2 
0 

1 
0 

3 
0 

4 
0 

6 
6 
6 
5 
5 
5 
5 
4 

6 
5 
4 
3 
3 
3 
3 
3 

6 
6 
6 
5 
4 
1 
0 

2 

3 

4 

5 

6 

7 

14 

More  accurate  determinations  showed  that  already  a  3/16  m 
NaCl  solution  renders  the  solution  of  2 . 2  c.c.  m/2  KCl  in  100  c.c. 
of  the  solution  harmless. 

It  was  next  determined  whether  different  concentrations  of 
KCl  required  different  concentrations  of  NaCl.  It  was  found 
that  the  coefficient  of  antagonization  KCl /NaCl  has  an  approxi- 
mately constant  value,  namely,  about  1/17,  as  the  following 
table  shows. 


184         The  Mechanistic  Conception  of  Life 

TABLE  IV 

CoeflQcient 

of  Antago- 

nization 

0.6  c.c.  m/2  KCl  rendered  harmless  in  100  c.c.  3/64  m  NaCL  . .  1/16 

0 . 7  c.c.  m/2  KCl  rendered  harmless  in  100  c.c.  4/64  m  NaCl . . .  1/18 

0.9  c.c.  m/2  KCl  rendered  harmless  in  100  c.c.  5/64  m  NaCl. . .  1/17 

1 . 0  c.c.  m/2  KCl  rendered  harmless  in  100  c.c.  5/64-6/64  m 

NaCl 1/16-1/19 

1 . 1  c.c.  m/2  KCl  rendered  harmless  in  100  c.c.  6/64  m  NaCl. . .  1/17 
1 . 65  c.c.  m/2  KCl  rendered  harmless  in  100  c.c.  5/32  m  NaCl. . .  1/19 

2.2  c.c.  m/2  KCl  rendered  harmless  in  100  c.c.  6/32  m  NaCl. . .  1/17 
2.75  c.c.  m/2  KCl  rendered  harmless  in  100  c.c.  7/32  m  NaCl. .  .1/16 

3 . 3  c.c.  m/2  KCl  rendered  harmless  in  100  c.c.  9/32  m  NaCl . . .  1/17 

What  happens  if  we  vary  this  ratio  ?  If  we  add  too  little 
NaCl  to  the  KCl  solution,  namely,  only  1  to  10  molecules  NaCl 
to  1  molecule  of  KCl,  the  solution  becomes  more  harmful  than 
if  KCl  is  alone  in  solution;  if  we  add  considerably  more  than  17 
molecules  NaCl,  e.g.,  50  molecules  to  one  molecule  of  KCl,  the 
solution  becomes  toxic  again;  and  the  more  so  the  higher  the 
concentration  of  NaCl.  This  indicates  that  the  antagonistic 
effect  requires  a  rather  definite  ratio  of  the  two  salts.  This 
furnishes  the  reason  why  an  m/2  solution  of  NaCl  can,  as  a  rule, 
not  be  rendered  completely  harmless  by  the  mere  addition  of 
KCl,  but  that  in  addition  CaClg  is  needed. 

If  we  add  to  100  c.c.  m/2  NaCl  enough  KCl  to  make  the 
ratio  KCl :  NaCl  =  1/17  we  find  that  the  antagonization  of  KCl : 
NaCl  becomes  incomplete.  If  the  amount  of  KCl  in  100  c.c. 
of  the  solution  exceeds  2.2  c.c.  m/2  KCl,  antagonization  is  still 
to  some  extent  possible,  but  it  becomes  more  incomplete  the 
higher  the  concentration  of  KCl.  For  this  reason  it  is  not 
possible  to  render  an  m/2  solution  of  NaCl  harmless  by  the 
mere  addition  of  KCl. 

CaCla  acts  upon  KCl  similarly  as  does  NaCl,  but  it 
acts  more  powerfully;  i.e.,  the  coefficient  of  antagonization, 
KCl/CaClg,  is  several  hundred  or  a  thousand  times  as  great 
as  that  of  KCl/NaCl,  as  the  following  tables  shows. 


Role  of  Salts  in  Preservation  of  Life      185 


TABLE  V 

Coefficient  of  Antago- 
nization  KCl/CaCU 

1 . 1    c.c.  m/2  KCl  in  100  c.c.  H^O  require  0 . 1  m/100  CaCL ....  550 

.165 
.366 
.137.5 
.103 


1.65  c.c.  ni/2  KCl  in  100  c.c.  H^O  require  0.5  m/100  CaCl, 

2.2  c.c.  m/2  KCl  in  100  c.c.  H^O  require  0.3  m/100  CaCL 
2.75  c.c.  m/2  KCl  in  100  c.c.  H.O  require  1.0  m/100  CaCl 

3.3  c.c.  m/2  KCl  in  100  c.c.  H^O  require  1.6  m/100  CaCL 

The  coefficients  are  not  as  regular  as  in  the  case  of  antagoni- 
zation  of  KCl  by  NaCl.  This  is  due  to  the  fact  that  the  minimal 
value  of  CaClg  at  which  it  renders  the  KCl  harmless  cannot 
be  determined  as  sharply  as  the  limit  for  NaCl.  Why  is  less 
CaCla  required  than  NaCl?  We  can  only  answer  with  a  sug- 
gestion first  offered  by  T.  B.  Robertson,  namely,  that  CaCl2 
produces  its  protective  effect  through  the  formation  of  a  com- 
paratively insoluble  compound  (in  this  case  on  the  gills  or  the 
rest  of  the  surface  of  the  animal)  while  NaCl  acts  through  the 
formation  of  a  compound  which  is  more  soluble.  This  view 
is  corroborated  by  the  observation  which  we  made,  that  Sr  is 
just  as  effective  to  antagonize  KCl  as  CaClg,  but  that  Mg 
is  much  less  efficient.  This  would  correspond  with  the  well- 
known  fact  that  many  strontium  salts  are  just  as  insoluble,  if 
not  more  insoluble,  than  the  calcium  salts,  while  the  magnesium 
salts  are  often  incomparably  more  soluble,  for  instance,  in  the 
case  of  the  sulphates.  BaClg  antagonizes  KCl  also  powerfully ^ 
but,  probably,  in  consequence  of  the  fact  that  the  substances 
formed  at  the  surface  of  the  animal  or  the  gills,  diffuse  slowly 
into  the  cells,  the  fish  do  not  remain  alive  as  long  if  Ba  is  used  as 
if  the  more  harmless  Ca  and  Sr  are  used. 

It  is  very  remarkable  that  CaCl,  renders  harmless  any  given 
concentration  of  KCl  below  6.6  c.c.  m/2  KCl  in  100  c.c.  of  the 
solution,  but  not  above  this  limit.  This  limit  is  exactly  the 
same  which  we  found  in  the  case  of  antagonization  of  KCl  by 
NaCl.  Even  the  combination  of  NaCl  and  CaClg  does  not 
permit  us  to  render  harmless  more  than  6.6  c.c.  m/2  KCl  in 
100  c.c.  of  the  solution. 


186         The  Mechanistic  Conception  of  Life 

If  we  try  to  render  NaCl  harmless  by  KCl  and  CaClg  we 
find  that  CaClg  can  antagonize  even  a  6/8  m  and  a  7/8  m  solu- 
tion of  NaCl,  while  KCl  ceases  to  show  any  antagonistic  effect 
if  the  NaCl  solution  exceeds  m/2  or  5/8  m. 

Experiments  with  pure  CaClg  solutions  give  the  result  that 
this  substance  is  harmless  in  a  solution  of  that  concentration  in 
which  this  salt  is  contained  in  the  sea-water.  Fundulus  can 
live  indefinitely  in  a  solution  of  1.5  c.c.  m/2  CaClg  in  100  c.c. 
Botanists  have  also  found  that  weak  solutions  of  CaClg  are 
comparatively  little  toxic.  This  gives  us  the  impression  that 
the  effect  upon  the  surface  film  of  protoplasm  produced  by 
CaCla  is  especially  important  for  the  protection  of  the  proto- 
plasm. This  conclusion  receives  an  indirect  support  by  the 
well-known  experiments  of  Herbst,  who  found  that  in  sea-water 
deprived  of  calcium  the  segmentation  cells  of  a  sea-urchin 
embryo  fall  apart  through  the  disintegration  or  liquefaction  of 
a  film  which  surrounds  the  embryo  and  keeps  the  cells  together. 
If  such  eggs  are  brought  back  into  solution  containing  calcium 
the  film  is  restored  and  the  cells  come  into  close  contact  again. 

It  is  therefore  not  impossible  that  the  mechanism  of  the 
antagonism  between  KCl  and  NaCl  is  similar  to  that  found 
between  NaCl  and  ZnSO^.  It  seems  only  due  to  the  high  con- 
centration of  the  NaCl  in  the  sea-water  and  in  the  blood  that, 
in  addition  to  KCl  and  NaCl,  CaClg  is  needed.  But  the  case 
is  not  so  unequivocal  as  the  previously  mentioned  cases  of 
antagonism  between  only  two  electrolytes. 

VIII 

It  is  necessary  for  our  understanding  of  the  life-preserving 
action  of  salts  that  we  do  not  depend  merely  on  conclusions 
drawn  from  experiments,  but  that  we  must  be  able  to  see 
directly  in  which  way  abnormal  salt  solutions  cause  the  death 
of  the  cell.     Such  an  opportunity  is  offered  us  through  the 


Role  of  Salts  in  Preservation  of  Life       187 

observation  of  the  eggs  of  the  sea-urchin.  If  we  put  the  ferti- 
Hzed  eggs  of  the  sea-urchin  into  an  abnormal  salt  solution,  a 
destruction  of  the  cell  gradually  takes  place.  The  destruction, 
as  a  rule,  begins  on  the  surface  of  the  protoplasm,  and  consists 
very  often  in  the  formation  and  falling  off  of  small  granules  or 
droplets.  This  process  gradually  continues  from  the  periphery 
toward  the  center  until  the  whole  egg  is  disintegrated.  For 
different  salt  solutions  the  picture  of  the  disintegration  is  a  little 
different,  but  sufficiently  characteristic  for  a  given  solution,  so 
that  if  one  become  familiar  with  these  pictures,  one  is  able  to 
diagnose  to  some  extent  the  nature  of  the  solution  from  the  way 
in  which  the  cell  disintegrates. 

This  process  of  disintegration  can  be  observed  if  the  eggs 
are  put  into  a  pure  solution  of  sodium  chloride,  or  in  a  mixture  of 
sodium  chloride  and  calcium  chloride,  or  in  a  mixture  of  sodium 
chloride  and  potassium  chloride.  If,  however,  all  three  salts 
are  used  in  the  proportion  in  which  they  occur  in  the  sea-water 
no  disintegration  takes  place  and  the  surface  of  the  egg  remains 
perfectly  smooth  and  normal.  One  gains  the  impression  as  if 
the  protoplasm  of  the  egg  were  held  together  by  a  continuous 
surface  film  of  a  definite  texture.  If  we  put  the  egg  into  an 
abnormal  solution  this  surface  film  is  modified  and  changed, 
and  the  change  of  the  surface  film  is  often  followed  by  a  gradual 
process  of  disintegration  of  the  rest  of  the  cell. 

These  observations  on  the  sea-urchin  egg,  therefore,  sug- 
gest the  possibility  that  the  combination  of  the  three  salts  in 
their  definite  proportion  and  concentration  has  the  function  of 
forming  a  surface  film  of  a  definite  structure  or  texture, 
around  the  protoplasm  of  each  cell,  by  which  the  protoplasm 
is  kept  together,  protected  against  and  separated  from  the 
surrounding  media. 

The  previously  mentioned  observation  of  Herbst  again 
shows  the  important  role  of  calcium  in  this  process. 


188         The  Mechanistic  Conception  of  Life 

IX 

The  objection  might  be  raised  that  the  beneficial  action  of 
the  three  salts  could  only  be  proved  on  marine  animals  or  on 
tissues  of  higher  animals,  which  are  said  to  be  "adapted"  to  a 
mixture  of  NaCl,  KCl,  and  CaCl2  in  definite  proportions. 
Experiments  on  fresh-water  organisms,  for  which  "adaptation" 
to  a  mixture  of  NaCl,  KCl,  and  CaClg  in  these  definite  propor- 
tions cannot  be  claimed,  show  that  this  objection  is  not  valid. 
Ostwald  worked  with  fresh-water  crustaceans  which  he  put  into 
mixtures  of  various  salts.  It  was  found  that  these  animals 
live  longer  in  a  mixture  of  NaCl+KCl+CaCla  than  in  a  solu- 
tion of  NaCl,  or  NaCl+KCl,  or  NaCl+CaCl^  of  the  same 
osmotic  pressure. 

Osterhout  was  able  to  show  that  the  spores  of  a  certain 
variety  of  Vaucheria  die  in  a  pure  3/32  m  solution  of  NaCl  in 
10  to  20  minutes,  while  they  live  in  100  c.c.  3/32  m  NaCl  +  1  c.c. 
3/32  CaCl^  2  to  4  weeks,  and  in  100  c.c.  3/32  m  NaCl+1  c.c. 
3/32  m  CaCl2+2.2  c.c.  3/32  m  KCl  6  to  8  weeks.  The  reac- 
tion of  the  solution  was  strictly  neutral  and  the  NaCl  the  purest 
obtainable.  The  results  remained  the  same  after  the  NaCl 
had  been  recrystallized  six  times.  Experiments  with  Spirogyra 
gave  a  similar  result.  The  solutions  were  all  3/32  m.  In 
NaCl  the  Spirogyra  died  in  18  hours;  in  NaCl + KCl  in  two 
days;  in  NaCl + KCl ^-CaCla  they  lived  65  days.  Osterhout 
caused  wheat  grains  to  develop  in  such  solutions  and  measured 
the  total  length  of  the  roots  formed. 

Total  Length  of 
Nature  of  the  Solution  Koots  after  40  Days 

H2O 740  mm. 

100  c.c.  3/25  NaCl 59  mm. 

100  c.c.  3/25  NaCl+2.0  3/25  CaCL 254  mm. 

100  c.c.  3/25  NaCl+2.0  3/25  CaCL+2.2  3/25  m  KCl 324  mm. 

These  cases,  to  which  many  other  similar  observations  might 
be  added,  prove  that  the  life-preserving  effect  of  the  combina- 
tion of  NaCl+KCl+CaCla  in  definite  proportions  is  not  due 


Role  of  Salts  in  Peeservation  of  Life       189 

to  the  fact  that  organisms  are  ''adapted"  to  this  mixture  but 
to  a  specific  protective  effect  of  the  combination  of  the  three 
salts  upon  the  cells. 

X 

It  seems,  therefore,  to  be  a  general  fact  that  wherever  tissues 
or  animals  require  a  medium  of  a  comparatively  high  osmotic 
pressure — like  our  tissues — ^their  life  lasts  much  longer  in  a 
mixture  of  NaCl+KCl+CaClg  in  the  proportion  in  which  these 
salts  exist  in  the  blood  and  in  the  ocean,  than  in  any  other 
osmotic  solution,  even  a  pure  solution  of  NaCl.  But  the  reader 
has  noticed  that  there  are  considerable  differences  in  the  resist- 
ance of  various  organisms  to  abnormal  solutions.  While  a  marine 
Gammarus  dies  in  half  an  hour  in  an  isotonic  solution  of  NaCl  or 
cane  sugar,  red  blood  corpuscles  or  even  the  muscle  of  a  frog  can 
be  kept  for  a  day  or  longer  in  such  a  solution  (of  course  even 
the  muscle  of  a  frog  lives  longer  if  the  NaCl  solution  contains  in 
addition  KCl  or  CaClg) .     What  causes  this  difference  ? 

Six  years  ago  I  found  that  the  unfertilized  eggs  of  the  sea- 
urchin  (Strongylocentrotus  purpuratus)  can  keep  alive  and 
remain  apparently  intact  in  a  pure  neutral  solution  of  CaClg 
or  of  NaCl  for  several  days  at  a  temperature  of  15°,  while  the 
fertilized  eggs  of  the  same  female  are  killed  in  a  pure  neutral 
solution  of  CaClg  in  a  few  hours.  The  same  difference  is  found 
for  other  salts  also.  What  causes  this  difference?  Several 
authors  have  suggested  that  it  is  due  to  the  fact  that  the 
fertilized  egg  is  more  permeable  to  salts  than  the  unfertilized 
egg.  But  recent  experiments  by  Warburg,  which  were  con- 
firmed and  amplified  by  Harvey,  make  it  doubtful  whether  the 
salts  which  are  not  soluble  in  fats  can  enter  the  fertilized  egg 
at  all.  I  believe  that  the  explanation  of  the  difference  is  much 
more  simple.  The  unfertilized  egg  is  surrounded  by  a  cortical 
layer  and  this  layer  is  destroyed  or  modified  in  the  process  of 
fertilization.  One  result  of  this  modification  is  the  formation 
of  the  fertilization  membrane,  for  which  I  have  been  able  to 


190         The  Mechanistic  Conception  of  Life 

show  that  it  is  readily  permeable  for  salts.  As  long  as  the 
cortical  layer  of  the  unfertilized  egg  is  intact,  it  prevents  the 
surrounding  salt  solution  from  coming  in  contact  with  the  proto- 
plasm or  at  least  it  retards  this  process.  If,  however,  the 
cortical  layer  is  destroyed  by  fertilization  the  surrounding 
salt  solution  comes  directly  in  contact  with  the  protoplasm  and 
if  the  solution  is  abnormal  it  can  cause  the  disintegration  of  the 
surface  layer  of  the  protoplasm. 

I  am  inclined  to  believe  that  differences  in  the  resisting 
power  of  various  cells  or  organisms  to  abnormal  salt  solutions  are 
primarily  due  to  differences  in  the  constitution  of  the  protective 
envelopes  of  the  animals  or  the  cells.  Microorganisms  which 
can  live  in  strong  organic  acids  or  salt  solutions  of  a  high 
concentration  probably  possess  a  surface  layer  which  shuts  off 
their  protoplasm  from  contact  with  the  solution.  For  the 
protoplasm  of  muscle  the  rather  tough  sarcolemma  forms  not 
an  absolute  but  nevertheless  an  effective  wall  against  the 
surrounding  solution. 

But  aside  from  differences  of  this  kind  there  are  other  condi- 
tions which  influence  the  degree  of  resistance  of  cells  to  various 
solutions.  I  have  found  that  the  fertilized  eggs  of  the  sea- 
urchin  will  live  longer  in  abnormal  salt  solutions  if  the  oxida- 
tions in  the  egg  are  stopped,  either  by  the  withdrawal  of  oxygen 
or  the  addition  of  KCN  or  NaCN.  Warburg  and  Meyerhof 
have  drawn  the  conclusion  that  in  a  pure  NaCl  solution  the 
rate  of  oxidations  of  the  egg  of  Strongylocentrotus  is  increased 
and  that  it  is  this  increase  in  the  rate  of  oxidations  which  kills 
the  eggs.  But  this  increase  of  oxidations  cannot  be  observed 
in  the  eggs  of  Arhacia  when  they  are  put  into  a  pure  NaCl  solu- 
tion and,  moreover,  lack  of  oxygen  prolongs  the  life  of  the 
fertilized  egg  just  as  well  in  solutions  of  NaCl+CaClg  or  of 
NaCl+BaClg,  for  which  salts  these  authors  do  not  claim  that 
they  can  raise  the  rate  of  oxidations  of  the  egg.  I  am  inclined 
to  believe  that  during  or  previously  to   cell-division,  besides 


Role  of  Salts  in  Preservation  of  Life       191 

phenomena  of  streaming  inside  the  cell,  changes  in  the  surface 
film  of  the  protoplasm  occur,  whereby  this  film  is  more  easily 
injured  by  the  salts.  If  we  suppress  the  oxidations  we  suppress 
also  the  processes  leading  to  cell-division  and  thereby  retard 
the  deleterious  action  of  the  abnormal  salt  solution  upon  the 
surface  layer  of  the  protoplasm  of  the  egg. 

XI 

If  we  now  raise  the  question  as  to  why  salts  are  necessary 
for  the  preservation  of  the  life  of  the  cell  we  can  point  to  a 
number  of  cases  in  which  this  answer  seems  clear.  Each  cell 
may  be  considered  a  chemical  factory,  in  which  the  work  can 
only  go  on  in  the  proper  way,  if  the  diffusion  of  substances 
through  the  cell- wall  is  restricted.  This  diffusion  depends  on 
the  nature  of  the  surface  layer  of  the  cell.  Overton  and  others 
assume  that  this  layer  consists  of  a  continuous  membrane  of 
fat  or  lipoids.  This  assumption  is  not  compatible  with  two 
facts,  namely,  that  water  diffuses  very  rapidly  into  the  cell, 
and  second,  that  life  depends  upon  an  exchange  of  water- 
soluble  and  not  of  fat-soluble  substances  between  the  cells 
and  the  surrounding  liquid.  The  above-mentioned  facts  of  the 
antagonism  between  acids  and  salts  suggest  the  idea  that  the 
surface  film  of  cells  consists  exclusively  or  essentially  of  certain 
proteins. 

The  experiments  mentioned  in  this  paper  indicate  that  the 
role  of  salts  in  the  preservation  of  life  consists  in  the  'banning" 
effect  which  they  have  upon  the  surface  films  of  the  cells, 
whereby  these  films  acquire  those  physical  qualities  of  dura- 
bility and  comparative  impermeability,  without  which  the  cell 
cannot  exist. 

On  this  assumption  we  can  understand  that  neutral  salts 
should  be  necessary  for  the  preservation  of  life  although  they 
do  not  furnish  energy. 

As  far  as  the  dynamical  effects  of  salts  are  concerned  it  is 


192         The  Mechanistic  Conception  of  Life 

not  impossible  that  some  of  them  belong  also  to  the  type  of 
those  mentioned  in  this  paper.  The  fact  that  the  addition  of 
calcium  to  an  NaCl  solution  prevents  the  twitchings  of  the 
muscle,  which  occur  in  the  pure  NaCl  solution,  suggests  the 
possibility  that  the  CaClg  merely  prevents  or  retards  the  diffu- 
sion of  NaCl  through  the  sarcolemma.  But  other  effects  of 
salts,  e.g.,  the  apparent  dependence  of  contractility  of  the 
muscle  upon  the  presence  of  NaCl,  or  the  role  of  PO^,  do  not 
find  their  explanation  in  the  facts  discussed  here. 


X.    EXPERIMENTAL    STUDY    OF    THE    INFLUENCE 
OF  ENVIRONMENT  ON  ANIMALS 


X 

EXPERIMENTAL  STUDY  OF  THE  INFLUENCE  OF 
ENVIRONMENT  ON  ANIMALS^ 

I.     INTRODUCTORY   REMARKS 

What  the  biologist  calls  the  natural  environment  of  an 
animal  is  from  a  physical  point  of  view  a  rather  rigid  combina- 
tion of  definite  forces.  It  is  obvious  that  by  a  purposeful  and 
systematic  variation  of  these  and  by  the  application  of  other 
forces  in  the  laboratory,  results  must  be  obtainable  which  do 
not  appear  in  the  natural  environment.  This  is  the  reasoning 
underlying  the  modern  development  of  the  study  of  the  effect 
of  environment  upon  animal  life.  It  was  perhaps  not  the  least 
important  of  Darwin's  services  to  science  that  the  boldness  of 
his  conceptions  gave  to  the  experimental  biologist  courage  to 
enter  upon  the  attempt  Of  controlling  at  will  the  life  phenomena 
of  animals,  and  of  bringing  about  effects  which  cannot  be 
expected  in  nature. 

The  systematic  physico-chemical  analysis  of  the  effect  of 
outside  forces  upon  the  form  and  reactions  of  animals  is  also 
our  only  means  of  unraveling  the  mechanism  of  heredity 
beyond  the  results  which  can  be  obtained  by  a  mere  cytological 
investigation.  The  manner  in  which  a  germ  cell  can  force  upon 
the  adult  certain  characters  will  not  be  understood  until  we 
succeed  in  varying  and  controlling  hereditary  characteristics; 
and  this  can  only  be  accomplished  on  the  basis  of  a  systematic 
study  of  the  effects  of  chemical  and  physical  forces  upon  living 
matter. 

Owing  to  limitation  of  space  this  sketch  is  necessarily  very 
incomplete,  and  it  must  not  be  inferred  that  studies  which  are 

1  Reprinted  from  Darwin  and  Modern  Science  (1909),  by  covirtesy  of  Professor 
A.  C.  Seward,  of  the  University  of  Cambridge,  England. 

195 


196         The  Mechanistic  Conception  of  Life 

not  mentioned  here  were  considered  to  be  of  minor  importance. 
All  the  writer  could  hope  to  do  was  to  bring  together  a  few 
instances  of  the  experimental  analysis  of  the  effect  of  environ- 
ment, which  indicate  the  nature  and  extent  of  our  control 
over  life  phenomena  and  which  also  have  some  relation  to  the 
work  of  Darwin.  In  the  selection  of  these  instances  preference 
is  given  to  those  problems  which  are  not  too  technical  for  the 
general  reader. 

The  forces,  the  influence  of  which  we  shall  discuss,  are  in 
succession  chemical  agencies,  temperature,  light,  and  gravita- 
tion. We  shall  also  treat  separately  the  effect  of  these  forces 
upon  form  and  instinctive  reactions. 

II.     THE   EFFECTS   OF   CHEMICAL  AGENCIES 

a)  Heterogeneous  hybridization. — It  was  held  until  recently 
that  hybridization  is  not  possible  except  between  closely  related 
species  and  that  even  among  these  a  successful  hybridization 
cannot  always  be  counted  upon.  This  view  was  well  supported 
by  experience.  It  is,  for  instance,  well  known  that  the  majority 
of  marine  animals  lay  their  unfertilized  eggs  in  the  ocean  and 
that  the  males  shed  their  sperm  also  into  the  sea-water.  The 
numerical  excess  of  the  spermatozoa  over  the  ova  in  the  sea- 
water  is  the  only  guaranty  that  the  eggs  are  fertilized,  for  the 
spermatozoa  are  carried  to  the  eggs  by  chance  and  are  not 
attracted  by  the  latter.  This  statement  is  the  result  of  numer- 
ous experiments  by  various  authors,  and  is  contrary  to  common 
belief.  As  a  rule  all  or  the  majority  of  individuals  of  a  species  in 
a  given  region  spawn  on  the  same  day,  and  when  this  occurs  the 
sea-water  constitutes  a  veritable  suspension  of  sperm.  It  has 
recently  been  shown  by  experiment  that  in  fresh  sea-water  the 
sperm  may  live  and  retain  its  fertilizing  power  for  several  days. 
It  is  thus  unavoidable  that  at  certain  periods  more  than  one  kind 
of  spermatozoa  is  suspended  in  the  sea-water  and  it  is  a  matter 
of  surprise  that  the  most  heterogeneous  hybridizations  do  not 


Influence  of  Environment  on  Animals       197 

constantly  occur.  The  reason  for  this  becomes  obvious  when 
we  bring  together  mature  eggs  and  equally  mature  and  active 
sperm  of  different  families.  When  this  is  done  no  egg  is,  as  a 
rule,  fertilized.  The  eggs  of  a  sea-urchin  can  be  fertihzed  by 
sperm  of  their  own  species,  or,  though  in  smaller  numbers,  by 
the  sperm  of  other  species  of  sea-urchins,  but  not  by  the  sperm 
of  other  groups  of  echinoderms,  e.g.,  star-fish,  brittle-stars, 
holothurians,  or  crinoids,  and  still  less  by  the  sperm  of  more 
distant  groups  of  animals.  The  consensus  of  opinion  seemed 
to  be  that  the  spermatozoon  must  enter  the  egg  through  a 
narrow  opening  or  canal,  the  so-called  micropyle,  and  that  the 
micropyle  allowed  only  the  spermatozoa  of  the  same  or  of  a 
closely  related  species  to  enter  the  egg. 

It  seemed  to  the  writer  that  the  cause  of  this  limitation  of 
hybridization  might  be  of  another  kind  and  that  by  a  change 
in  the  constitution  of  the  sea-water  it  might  be  possible  to 
bring  about  heterogeneous  hybridizations,  which  in  normal 
sea-water  are  impossible.  This  assumption  proved  correct. 
Sea-water  has  a  faintly  alkaline  reaction  (in  terms  of  the  physi- 
cal chemist  its  concentration  of  hydroxy  1  ions  is  about  10""^  n 
at  Pacific  Grove,  California,  and  about  lO"^  n  at  Woods  Hole, 
Massachusetts).  If  we  slightly  raise  the  alkalinity  of  the  sea- 
water  by  adding  to  it  a  small  but  definite  quantity  of  sodium 
hydroxide  or  some  other  alkali,  the  eggs  of  the  sea-urchin 
can  be  fertilized  with  the  sperm  of  widely  different  groups  of 
animals.  In  1903  it  was  shown  that  if  we  add  from  about  0.5 
to  0.8  c.c.  n/10  sodium  hydroxide  to  50  c.c.  of  sea-water,  the 
eggs  of  Strongylocentrotus  purpuratus  (a  sea-urchin  which  is 
found  on  the*  coast  of  California)  can  be  fertilized  in  large 
quantities  by  the  sperm  of  various  kinds  of  star-fish,  brittle- 
stars,  and  holothurians;  while  in  normal  sea-water  or  with 
less  sodium  hydroxide  not  a  single  egg  of  the  same  female  could 
be  fertilized  with  the  star-fish  sperm  which  proved  effective 
in  the  hyperalkaline  sea-water.    The  sperm  of  the  various  forms 


198         The  Mechanistic  Conception  of  Life 

of  star-fish  was  not  equally  effective  for  these  hybridizations; 
the  sperm  of  Asterias  ochracea  and  A.  capitata  gave  the  best 
results,  since  it  was  possible  to  fertilize  from  50  per  cent  to 
100  per  cent  of  the  sea-urchin  eggs,  while  the  sperm  of  Pycno- 
podia  and  Asterina  fertilized  only  10  or  2  per  cent  respectively 
of  the  same  eggs. 

Godlewski  used  the  same  method  for  the  hybridization  of 
the  sea-urchin  eggs  with  the  sperm  of  a  crinoid  {Antedon 
rosacea) .  Kupelwieser  afterward  obtained  results  which  seemed 
to  indicate  the  possibility  of  fertilizing  the  eggs  of  Strongylo- 
centrotus  with  the  sperm  of  a  mollusk  (Mytilus).  Recently,  the 
writer  succeeded  in  fertilizing  the  eggs  of  Strongylocentrotus 
franciscanus  with  the  sperm  of  a  mollusk — Chlorostoma.  This 
result  could  only  be  obtained  in  sea-water  the  alkalinity  of 
which  had  been  increased  (through  the  addition  of  0.8  c.c.  n/10 
sodium  hydroxide  to  50  c.c.  of  sea- water).  We  thus  see  that 
by  increasing  the  alkalinity  of  the  sea-water  it  is  possible  to 
effect  heterogeneous  hybridizations  which  are  at  present  impos- 
sible in  the  natural  environment  of  these  animals. 

It  is,  however,  conceivable  that  in  former  periods  of  the 
earth's  history  such  heterogeneous  hybridizations  were  possible. 
It  is  known  that  in  solutions  like  sea-water  the  degree  of  alkalin- 
ity must  increase  when  the  amount  of  carbon  dioxide  in  the 
atmosphere  is  diminished.  If  it  be  true,  as  Arrhenius  assumes, 
that  the  Ice  age  was  caused  or  preceded  by  a  diminution  in  the 
amount  of  carbon  dioxide  in  the  air,  such  a  diminution  must  also 
have  resulted  in  an  increase  of  the  alkalinity  of  the  sea-water, 
and  one  result  of  such  an  increase  must  have  been  to  render 
possible  heterogeneous  hybridizations  in  the  ocean  which  in  the 
present  state  of  alkalinity  are  practically  excluded. 

But  granted  that  such  hybridizations  were  possible,  would 
they  have  influenced  the  character  of  the  fauna?  In  other 
words,  are  the  hybrids  between  sea-urchin  and  star-fish,  or  better 
still,  between  sea-urchin  and  mollusks,  capable  of  development, 


Influence  of  Environment  on  Animals       199 

and  if  so,  what  is  their  character  ?  In  all  cases  of  heterogeneous 
hybridization  the  vitality  of  the  egg  or  the  embryo  seems 
weakened  and  it  is  still  doubtful  whether  any  heterogeneous 
hybrid  can  reach  maturity.  The  number  of  experiments  is  still 
limited  and  this  statement  is  therefore  not  yet  final. 

So  far  as  the  question  of  heredity  is  concerned,  all  the 
experiments  on  heterogeneous  hybridization  of  the  egg  of 
the  sea-urchin  with  the  sperm  of  star-fish,  brittle-stars,  crinoids, 
and  mollusks  have  led  to  the  same  result,  namely,  that  the  larvae 
have  purely  maternal  characteristics  and  differ  in  no  way  from 
the  pure  breed  of  the  form  from  which  the  egg  is  taken.  By  way 
of  illustration  it  may  be  said  that  the  larvae  of  the  sea-urchin 
reach  on  the  third  day  or  earlier  (according  to  species  and 
temperature)  the  so-called  pluteus  stage,  in  which  they  possess 
a  typical  skeleton  (Fig.  10,  p.  11);  while  neither  the  larvae 
of  the  star-fish  nor  those  of  the  mollusk  form  a  skeleton  at  the 
corresponding  stage.  It  was,  therefore,  a  matter  of  some 
interest  to  find  out  whether  or  not  the  larvae  produced  by  the 
fertiUzation  of  the  sea-urchin  egg  with  the  sperm  of  star-fish 
or  mollusk  would  form  the  normal  and  typical  pluteus  skeleton. 
This  was  invariably  the  case  in  the  experiments  of  Godlewski, 
Kupelwieser,  Hagedoorn,  and  the  writer.  These  hybrid  larvae 
were  exclusively  maternal  in  character. 

It  might  be  argued  that  in  the  case  of  heterogeneous  hybridi- 
zation the  sperm  nucleus  does  not  fuse  with  the  egg  nucleus,  and 
that,  therefore,  the  spermatozoon  cannot  transmit  its  hereditary 
substances  to  the  larvae.  But  these  objections  are  refuted 
by  Godlewski's  experiments,  in  which  he  showed  definitely  that 
if  the  egg  of  the  sea-urchin  is  fertilized  with  the  sperm  of  a 
crinoid  the  fusion  of  the  egg  nucleus  and  sperm  nucleus  takes 
place  in  the  normal  way. 

h)  Artificial  parthenogenesis. — Possibly  in  no  other  field  of 
biology  has  our  ability  to  control  life  phenomena  by  outside 
conditions  been  proved  to  such  an  extent  as  in  the  domain  of 


200         The   Mechanistic  Conception  of  Life 

fertilization.  The  reader  knows  that  the  eggs  of  the  over- 
whelming majority  of  animals  cannot  develop  miless  a  sperma- 
tozoon enters  them.  In  this  case  a  living  agency  is  the  cause  of 
development  and  the  problem  arises  whether  it  is  possible  to 
accomplish  the  same  result  through  the  application  of  well- 
known  physico-chemical  agencies.  This  is,  indeed,  true,  and 
during  the  last  ten  years  living  larvae  have  been  produced  by 
chemical  agencies  from  the  unfertilized  eggs  of  sea-urchins, 
star-fish,  holothurians,  and  a  number  of  annelids  and  mollusks ; 
in  fact  this  holds  true  in  regard  to  the  eggs  of  practically  all 
forms  of  animals  with  which  such  experiments  have  been  tried 
long  enough.  In  each  form  the  method  of  procedure  is  some- 
what different  and  a  long  series  of  experiments  is  often  required 
before  the  successful  method  is  found. 

The  facts  of  artificial  parthenogenesis,  as  the  chemical 
fertilization  or  activation  of  the  egg  is  called,  have,  perhaps, 
some  bearing  on  the  problem  of  evolution.  If  we  wish  to  form 
a  mental  image  of  the  process  of  evolution  we  have  to  reckon 
with  the  possibility  that  parthenogenetic  propagation  may  have 
preceded  sexual  reproduction.  This  suggests  also  the  possi- 
bility that  at  that  period  outside  forces  may  have  supplied  the 
conditions  for  the  development  of  the  egg  which  at  present  the 
spermatozoon  has  to  supply.  For  this,  if  for  no  other  reason,  a 
brief  consideration  of  the  means  of  artificial  parthenogenesis 
may  be  of  interest  to  the  student  of  evolution. 

It  seemed  necessary  in  these  experiments  to  imitate  as 
completely  as  possible  by  chemical  agencies  the  effects  of  the 
spermatozoon  upon  the  egg.  When  a  spermatozoon  enters  the 
egg  of  a  sea-urchin  or  certain  star-fish  or  annelids,  the  immediate 
effect  is  a  characteristic  change  of  the  surface  of  the  egg,  namely, 
the  formation  of  the  so-called  membrane  of  fertihzation  (Figs. 
1  and  2).  The  writer  found  that  we  can  produce  this  mem- 
brane in  the  unfertilized  egg  by  certain  acids,  especially  the 
monobasic  acids  of  the  fatty  series,  e.g.,  formic,  acetic,  propionic, 


Influence  of  Environment  on  Animals       201 

butyric,  etc.  Carbon  dioxide  is  also  very  efficient  in  this 
direction.  It  was  also  found  that  the  higher  acids  are  more 
efficient  than  the  lower  ones,  and  it  is  possible  that  the  sperma- 
tozoon induces  membrane  formation  by  carrying  into  the  egg  a 
higher  fatty  acid,  namely  oleic  acid  or  one  of  its  salts  or  esters. 

The  physico-chemical  process  which  underlies  the  formation 
of  the  membrane  seems  to  be  the  cause  of  the  development  of  the 
egg.  In  all  cases  in  which  the  unfertilized  egg  has  been  treated 
in  such  a  way  as  to  cause  it  to  form  a  membrane  it  begins  to 
develop.  For  the  eggs  of  certain  animals  membrane  formation 
is  all  that  is  required  to  induce  a  complete  development  of  the 
unfertilized  egg,  e.g.,  in  the  star-fish  and  certain  annelids. 
For  the  eggs  of  other  animals  a  second  treatment  is  necessary. 
Thus  the  unfertilized  eggs  of  the  sea-urchin  Strongylocentrotus 
purpuratus  of  the  Californian  coast  begin  to  develop  when 
membrane  formation  has  been  induced  by  treatment  with  a 
fatty  acid,  e.g.,  butyric  acid;  but  the  development  soon  ceases 
and  the  eggs  perish  in  the  early  stages  of  segmentation,  or  after 
the  first  nuclear  division.  But  if  we  treat  the  same  eggs  after 
membrane  formation,  for  from  thirty-five  to  fifty-five  minutes 
(at  15°  C.)  with  sea-water  the  concentration  (osmotic  pressure) 
of  which  has  been  raised  through  the  addition  of  a  definite 
amount  of  some  salt  or  sugar,  the  eggs  will  segment  and  develop 
normally,  when  transferred  back  to  normal  sea-water.  If  care 
is  taken,  practically  all  the  eggs  can  be  caused  to  develop  into 
plutei,  the  majority  of  which  may  be  perfectly  normal  and  may 
live  as  long  as  larvae  produced  from  eggs  fertilized  with  sperm. 

It  is  possible  that  the  sea-urchin  egg  is  injured  in  the  process 
of  membrane  formation.  The  nature  of  this  injury  became 
clear  when  it  was  discovered  that  all  the  agencies  which  cause 
hemolysis,  i.e.,  the  destruction  of  the  red  blood  corpuscles,  also 
cause  membrane  formation  in  unfertilized  eggs,  e.g.,  fatty  acids 
or  ether,  alcohols  or  chloroform,  etc.,  or  saponin,  solanin, 
digitalin,   bile   salts,    and   alkali.     It   thus   happens  that  the 


202         The  Mechanistic  Conception  of  Life 

phenomena  of  artificial  parthenogenesis  are  Unked  together  with 
the  phenomena  of  hemolysis  which  at  present  play  so  important 
a  role  in  the  study  of  immunity.  The  difference  between 
cytolysis  (or  hemolysis)  and  fertilization  seems  to  be  this,  that 
the  latter  is  caused  by  a  superficial  cytolysis  of  the  egg,  while  if 
the  cytolytic  agencies  have  time  to  act  on  the  whole  egg  the 
latter  is  completely  destroyed.  If  we  put  unfertilized  eggs  of  a 
sea-urchin  into  sea-water  which  contains  a  trace  of  saponin  we 
notice  that,  after  a  few  minutes,  all  the  eggs  form  the  typical 
membrane  of  fertilization.  If  the  eggs  are  then  taken  out  of  the 
saponin  solution,  freed  from  all  traces  of  saponin  by  repeated 
washing  in  normal  sea-water,  and  transferred  to  the  hypertonic 
sea-water  for  from  thirty-five  to  fifty-five  minutes,  they  develop 
into  larvae.  If,  however,  they  are  left  in  the  sea-water  con- 
taining the  saponin  they  undergo,  a  few  minutes  after  membrane 
formation,  the  disintegration  known  in  pathology  as  cytolysis. 
Membrane  formation  is,  therefore,  caused  by  a  superficial  or 
incomplete  cytolysis.  It  is  possible  that  the  subsequent  treat- 
ment of  the  egg  with  hypertonic  sea-water  is  partly  needed  to 
overcome  the  destructive  effects  of  this  cytolysis  of  the  cortical 
layer. 

Many  pathologists  assume  that  hemolysis  or  cytolysis  is 
due  to  a  liquefaction  of  certain  fatty  or  fat-like  compounds, 
the  so-called  lipoids,  in  the  cell.  If  this  view  is  correct,  it 
would  be  necessary  to  ascribe  the  fertilization  of  the  egg  to  the 
same  process. 

The  analogy  between  hemolysis  and  fertilization  throws, 
possibly,  some  light  on  a  curious  observation.  It  is  well  known 
that  the  blood  corpuscles,  as  a  rule,  undergo  cytolysis  if  injected 
into  the  blood  of  an  animal  which  belongs  to  a  different  family. 
The  writer  found  last  year  that  the  blood  of  mammals,  e.g.,  the 
rabbit,  pig,  and  cattle,  causes  the  egg  of  Strongylocentrotus  to 
form  a  typical  fertilization  membrane.  If  such  eggs  are  after- 
ward treated  for  a  short  period  with  hypertonic  sea-water  they 


Influence  of  Environment  on  Animals       203 

develop  into  normal  larvae  (plutei) .  Some  substance  contained 
in  the  blood  causes,  presumably,  a  superficial  cytolysis  of  the 
egg  and  thus  starts  its  development. 

We  can  also  cause  the  development  of  the  sea-urchin  egg 
without  membrane  formation.  The  early  experiments  of  the 
writer  were  done  in  this  way  and  many  experimenters  still  use 
such  methods.  It  is  probable  that  in  this  case  the  mechanism 
of  fertilization  is  essentially  the  same  as  in  the  case  where  the 
membrane  formation  is  brought  about,  with  this  difference 
only,  that  the  cytolytic  effect  is  less  when  no  fertilization 
membrane  is  formed.  This  inference  is  corroborated  by 
observations  on  the  fertilization  of  the  sea-urchin  egg  with  ox 
blood.  It  very  frequently  happens  that  not  all  of  the  eggs  form 
membranes  in  this  process.  Those  eggs  which  form  membranes 
begin  to  develop,  but  perish  if  they  are  not  treated  with  hyper- 
tonic sea-water.  Some  of  the  other  eggs,  however,  which  do  not 
form  membranes,  develop  directly  into  normal  larvae  without 
any  treatment  with  hypertonic  sea-water,  provided  they  are 
exposed  to  the  blood  for  only  a  few  minutes.  Presumably  some 
blood  enters  the  eggs  and  causes  the  cytolytic  effects  in  a  less 
degree  than  is  necessary  for  membrane  formation,  but  in  a 
sufficient  degree  to  cause  their  development.  The  slightness 
of  the  cytolytic  effect  allows  the  egg  to  develop  without  treat- 
ment with  hypertonic  sea-water. 

Since  the  entrance  of  the  spermatozoon  causes  that  degree 
of  cytolysis  which  leads  to  membrane  formation,  it  is  probable 
that,  in  addition  to  the  cytolytic  or  membrane-forming  sub- 
stance (presumably  a  higher  fatty  acid),  it  carries  another 
substance  into  the  egg  which  counteracts  the  deleterious  effects 
underlying  or  following  membrane  formation. 

The  question  may  be  raised  whether  the  larvae  produced 
by  artificial  parthenogenesis  can  reach  the  mature  stage.  This 
question  may  be  answered  in  the  affirmative,  since  Delage  has 
succeeded  in  raising  several  parthenogenetic  sea-urchin  larvae 


204         The  Mechanistic  Conception  of  Life 

beyond  the  metamorphosis  into  the  adult  stage  and  since  in  all 
the  experiments  made  by  the  writer  the  parthenogenetic  plutei 
lived  as  long  as  the  plutei  produced  from  fertilized  eggs. 

c)  On  the  production  of  twins  from  one  egg  through  a  change 
in  the  chemical  constitution  of  the  sea-water. — The  reader  is 
probably  familiar  with  the  fact  that  there  exist  two  different 
types  of  human  twins.  In  the  one  type  the  twins  differ  as 
much  as  two  children  of  the  same  parents  born  at  different 
periods ;  they  may  or  may  not  have  the  same  sex.  In  the  second 
type  the  twins  have  invariably  the  same  sex  and  resemble  each 
other  most  closely.  Twins  of  the  latter  type  are  produced  from 
the  same  egg,  while  twins  of  the  former  type  are  produced 
from  two  different  eggs. 

The  experiments  of  Driesch  and  others  have  taught  us  that 
twins  originate  from  one  egg  in  this  manner,  namely,  that  the 
first  two  cells  into  which  the  egg  divides  after  fertilization 
become  separated  from  each  other.  This  separation  can  be 
brought  about  by  a  change  in  the  chemical  constitution  of 
the  sea-water.  Herbst  observed  that  if  the  fertilized  eggs  of  the 
sea-urchin  are  put  into  sea-water  which  is  freed  from  calcium, 
the  cells  into  which  the  egg  divides  have  a  tendency  to  fall 
apart.  Driesch  afterward  noticed  that  eggs  of  the  sea-urchin 
treated  with  sea-water  which  is  free  from  lime  have  a  tendency 
to  give  rise  to  twins.  The  writer  has  recently  found  that  twins 
can  be  produced  not  only  by  the  absence  of  lime,  but  also 
through  the  absence  of  sodium  or  of  potassium;  in  other  words, 
through  the  absence  of  one  or  two  of  the  three  important 
metals  in  the  sea-water.  There  is,  however,  a  second  condition, 
namely  that  the  solution  used  for  the  production  of  twins  must 
have  a  neutral  or  at  least  not  an  alkaline  reaction. 

The  procedure  for  the  production  of  twins  in  the  sea-urchin 
egg  consists  simply  in  this:  the  eggs  are  fertilized  as  usual  in 
normal  sea-water  and  then,  after  repeated  washing  in  a  neutral 
solution  of  sodium  chloride  (of  the  concentration  of  the  sea- 


Influence  of  Environment  on  Animals       205 

water),  are  placed  in  a  neutral  mixture  of  potassium  chloride 
and  calcium  chloride,  or  of  sodium  chloride  and  potassium 
chloride,  or  of  sodium  chloride  and  calcium  chloride,  or  of 
sodium  chloride  and  magnesium  chloride.  The  eggs  must 
remain  in  this  solution  until  half  an  hour  or  an  hour  after  they 
have  reached  the  two-cell  stage.  They  are  then  transferred 
into  normal  sea-water  and  allowed  to  develop.  From  50  to  90 
per  cent  of  the  eggs  of  Strongylocentrotus  purpuratus  treated  in 
this  manner  may  develop  into  twins.  These  twins  may  remain 
separate  or  grow  partially  together  and  form  double  monsters, 
or  heal  together  so  completely  that  only  slight  or  even  no 
imperfections  indicate  that  the  individual  started  its  career  as  a 
pair  of  twins.  It  is  also  possible  to  control  the  tendency  of  such 
twins  to  grow  together  by  a  change  in  the  constitution  of  the 
sea-water.  If  we  use  as  a  twin-producing  solution  a  mixture 
of  sodium,  magnesium,  and  potassium  chlorides  (in  the  propor- 
tion in  which  these  salts  exist  in  the  sea-water)  the  tendency 
of  the  twins  to  grow  together  is  much  more  pronounced  than  if 
we  use  simply  a  mixture  of  sodium  chloride  and  magnesium 
chloride. 

The  mechanism  of  the  origin  of  twins,  as  the  result  of  alter- 
ing the  composition  of  the  sea-water,  is  revealed  by  observation 
of  the  first  segmentation  of  the  egg  in  these  solutions.  This 
cell-division  is  modified  in  a  way  which  leads  to  a  separation 
of  the  first  two  cells  (see  Figs.  55  to  57).  If  the  egg  is  afterward 
transferred  back  into  normal  sea-water,  each  of  these  two  cells 
develops  into  an  independent  embryo.  Since  normal  sea-water 
contains  all  three  metals,  sodium,  calcium,  and  potassium,  and 
since  it  has  besides  an  alkaline  reaction,  we  perceive  the  reason 
why  twins  are  not  normally  produced  from  one  egg.  These 
experiments  suggest  the  possibility  of  a  chemical  cause  for  the 
origin  of  twins  from  one  egg  or  of  double  monstrosities  in  mam- 
mals. If,  for  some  reason,  the  liquids  which  surround  the 
human  egg  a  short  time  before  and  after  the  first  cell-division 


206 


The  Mechanistic  Conception  of  Life 


are  slightly  acid,  and  at  the  same  time  lacking  in  one  of  the 
three  important  metals,  the  conditions  for  the  separation  of 


Fig.  51 


Fig.  52 


Fig.  53 


Fig.  54 


Figs.  51-54. — CeU-division  in  a  sea-lircllin  egg,  Strongylocentrotus  purpura- 
tus,  in  normal  sea-water.  This  type  of  cell-division  leads  to  the  formation  of  one 
embryo  from  an  egg.  M  is  the  fertilization  membrane,  P  a  layer  of  colloidal 
substance  which  seems  to  serve  the  purpose  of  keeping  all  the  cells  of  an  egg 
together. 

the  first  two  cells  and  the  formation  of  identical  twins  are 
provided. 


Fig.  55 


Fig.  56 


Fig.  57 


Fig.  58 


Figs.  55-58. — Cell-division  in  the  egg  of  Strongylocentrotus  purpuratus 
which  leads  to  the  formation  of  twins.  This  ceU-di vision  can  be  observed  if  the 
egg  is  put  after  fertilization  into  a  neutral  mixture  of  salts  in  which  either  KCl, 
or  CaClz,  or  NaCl  is  lacking. 

In  such  a  neutral  solution  the  substance  which  forms  the  elastic  layer  {PM, 
Fig.  51)  is  dissolved.  During  the  segmentation  the  protoplasm  of  the  egg  spreads 
until  its  long  axis  touches  the  fertilization  membrane.  The  two  daughter-ceUs 
formed  (Fig.  57)  are  separated  from  each  other,  instead  of  remaining  connected 
as  in  the  normal  cell-division  (Fig.  53) .  If  about  one  hour  later  the  eggs  are  put 
back  into  normal  sea-water  each  of  the  two  cells  develops  into  an  embryo  (Fig.  58), 
and  the  egg  thus  gives  rise  to  two  instead  of  to  one  embryo. 


In  conclusion  it  may  be  pointed  out  that  the  reverse  result, 
namely,  the  fusion  of  normally  double  organs,  can  also  be 
brought  about  experimentally  through  a  change  in  the  chemical 
constitution  of  the  sea-water.     Stockard  succeeded  in  causing 


Influence  of  Envieonment  on  Animals       207 

the  two  eyes  of  a  fish  embryo  {Fundulus  heteroclitus)  to  fuse  into 
a  single  cyclopean  eye  through  the  addition  of  magnesium 
chloride  to  the  sea-water.  When  he  added  about  6  grams  of 
magnesium  chloride  to  100  c.c.  of  sea-water  and  placed  the 
fertilized  eggs  in  the  mixture,  about  50  per  cent  of  the  eggs  gave 
rise  to  one-eyed  embryos. 

When  the  embryos  were  studied  the  one-eyed  condition  was  found 
to  result  from  the  union  or  fusion  of  the  '^Anlagen"  of  the  two  eyes. 
Cases  were  observed  which  showed  various  degrees  in  this  fusion;  it 
appeared  as  though  the  optic  vesicles  were  formed  too  far  forward 
and  ventral,  so  that  their  antero-ventro-median  surfaces  fused.  This 
produces  one  large  optic  cup,  which  in  all  cases  gives  more  or  less 
evidence  of  its  double  nature.^ 

We  have  confined  ourselves  to  a  discussion  of  rather  simple 
effects  of  the  change  in  the  constitution  of  the  sea-water  upon 
development.  It  is  a  priori  obvious,  however,  that  an  unlimited 
number  of  pathological  variations  might  be  produced  by  a 
variation  in  the  concentration  and  constitution  of  the  sea-water, 
and  experience  confirms  this  statement.  As  an  example  we 
may  mention  the  abnormalities  observed  by  Herbst  in  the 
development  of  sea-urchins  through  the  addition  of  lithium  to 
sea-water.  It  is,  however,  as  yet  impossible  to  connect  in  a 
rational  way  the  effects  produced  in  this  and  similar  cases  with 
the  cause  which  produced  them;  and  it  is  also  impossible  to 
define  in  a  simple  way  the  character  of  the  change  produced. 

III.      THE    INFLUENCE    OF   TEMPERATUKE 

a)  The  influence  of  temperature  upon  the  density  of  pelagic 
organisms  and  the  duration  of  life. — It  has  often  been  noticed 
by  explorers  who  have  had  a  chance  to  compare  the  faunas  in 
different  climates  that  in  the  polar  seas  such  species  as  thrive 
at  all  in  those  regions  occur,  as  a  rule,  in  much  greater  density 
than  they  do  in  the  moderate  or  warmer  regions  of  the  ocean. 
This  refers  to  those  members  of  the  fauna  which  live  at  or  near 

1  Stockard,  Archiv  f.  Entwicklungsmechanik,  XXIII,  249,  1907. 


208         The  Mechanistic  Conception  of  Life 

the  surface,  since  they  alone  lend  themselves  to  a  statistical 
comparison.  In  his  account  of  the  Valdivia  expedition,  Chun^ 
calls  especial  attention  to  this  quantitative  difference  in  the 
surface  fauna  and  flora  of  different  regions.  ''In  the  icy  water 
of  the  Antarctic,  the  temperature  of  which  is  below  0°  C,  we 
find  an  astonishingly  rich  animal  and  plant  life.  The  same 
condition  with  which  we  are  familiar  in  the  Arctic  seas  is 
repeated  here,  namely,  that  the  quantity  of  plankton  material 
exceeds  that  of  the  temperate  and  warm  seas."  And  again,  in 
regard  to  the  pelagic  fauna  in  the  region  of  the  Kerguelen 
Islands,  he  states:  ''The  ocean  is  alive  with  transparent  jelly 
fish,  Ctenophores  {Bolina  and  Callianira)  and  of  Siphonophore 
colonies  of  the  genus  Agalma.^' 

The  paradoxical  character  of  this  general  observation  lies 
in  the  fact  that  a  low  temperature  retards  development,  and 
hence  should  be  expected  to  have  the  opposite  effect  from  that 
mentioned  by  Chun,  Recent  investigations  have  led  to  the 
conclusion  that  life  phenomena  are  affected  by  temperature  in 
the  same  sense  as  the  velocity  of  chemical  reactions.  In  the 
case  of  the  latter  van't  Hoff  had  shown  that  a  decrease  in 
temperature  by  10  degrees  reduces  their  velocity  to  one-half 
or  less,  and  the  same  has  been  found  for  the  influence  of  tempera- 
ture on  the  velocity  of  physiological  processes.  Thus  Snyder 
and  T.  B.  Robertson  found  that  the  rate  of  heart  beat  in  the 
tortoise  and  in  Daphnia  is  reduced  to  about  one-half  if  the 
temperature  is  lowered  10°  C,  and  Maxwell,  Keith  Lucas,  and 
Snyder  found  the  same  influence  of  temperature  for  the  rate 
with  which  an  impulse  travels  in  the  nerve.  Peter  observed 
that  the  rate  of  development  in  a  sea-urchin's  egg  is  reduced 
to  less  than  one-half  if  the  temperature  (within  certain  limits) 
is  reduced  by  10  degrees.  The  same  effect  of  temperature  upon 
the  rate  of  development  holds  for  the  egg  of  the  frog,  as  Cohen 
and  Peter  calculated  from  the  experiments  of  0.   Hertwig. 

1  Chun,  Aus  den  Tiefen  des  Weltmeeres,  p.  225,  Jena,  1903. 


Influence  of  Environment  on  Animals       209 

The  writer  found  the  same  temperature  coefficient  for  the  rate 
of  maturation  of  the  egg  of  a  moUusk  (Lottia). 

All  these  facts  prove  that  the  velocity  of  development  of 
animal  life  in  Arctic  regions,  where  the  temperature  is  near  the 
freezing  point  of  water,  must  be  from  two  to  three  times  smaller 
than  in  regions  where  the  temperature  of  the  ocean  is  about 
10°  C,  and  from  four  to  nine  times  smaller  than  in  seas  the 
temperature  of  which  is  about  20°  C.  It  is,  therefore,  exactly 
the  reverse  of  what  we  should  expect  when  authors  state  that 
the  density  of  organisms  at  or  near  the  surfac  e  of  the  ocean  in 
polar  regions  is  greater  than  in  more  temperate  regions. 

The  writer  believes  that  this  paradox  finds  its  explanation 
in  experiments  which  he  has  recently  made  on  the  influence 
of  temperature  on  the  duration  of  life  of  cold-blooded  marine 
animals.  The  experiments  were  made  on  the  fertilized  and 
unfertilized  eggs  of  the  sea-urchin,  and  yielded  the  result  that 
for  the  lowering  of  temperature  by  1°  C,  the  duration  of  life 
was  about  doubled.  Lowering  the  temperature  by  10  degrees 
therefore  prolongs  the  life  of  the  organism  2^°,  i.e.,  over  a  thou- 
sand times,  and  a  lowering  by  20  degrees  prolongs  it  about  one 
million  times.  Since  this  prolongation  of  life  is  far  in  excess 
of  the  retardation  of  development  through  a  lowering  of 
temperature,  it  is  obvious  that,  in  spite  of  the  retardation 
of  development  in  Arctic  seas,  animal  life  must  be  denser 
there  than  in  temperate  or  tropical  seas.  The  excessive 
increase  of  the  duration  of  life  at  the  poles  will  necessitate 
the  simultaneous  existence  of  more  successive  generations  of 
the  same  species  in  these  regions  than  in  the  temperate  or 
tropical  regions.^ 

The  writer  is  inclined  to  believe  that  these  results  have 
some  bearing  upon  a  problem  which  plays  an  important  role 
in  theories  of  evolution,  namely,  the  cause  of  natural  death. 

1  The  high  coeflacient  of  temperature  of  the  duration  of  life  may  possibly  only 
be  found  near  the  upper  temperature  limit  for  the  life  of  organisms.  But  tbis  is 
sufficient  for  our  theory. 


210         The  Mechanistic  Conception  of  Life 

It  has  been  stated  that  the  processes  of  differentiation  and 
development  lead  also  to  the  natural  death  of  the  individual.^ 
If  we  express  this  in  chemical  terms  it  means  that  the  chemical 
processes  which  underlie  development  also  determine  natural 
death.  Physical  chemistry  has  taught  us  to  identify  two  chemi- 
cal processes  even  if  only  certain  of  their  features  are  known. 
One  of  these  means  of  identification  is  the  temperature 
coefficient.  When  two  chemical  processes  are  identical,  their 
velocity  must  be  reduced  by  the  same  amount  if  the  tempera- 
ture is  lowered  to  the  same  extent.  The  temperature  coefficient 
for  the  duration  of  life  of  cold-blooded  organisms  seems,  how- 
ever, to  differ  enormously  from  the  temperature  coefficient  for 
their  rate  of  development.  For  a  difference  in  temperature  of 
10°  C,  the  duration  of  life  is  altered  five  hundred  times  as  much 
as  the  rate  of  development;  and,  for  a  change  of  20°  C,  it  is 
altered  more  than  a  hundred  thousand  times  as  much.  From 
this  we  may  conclude  that,  at  least  for  the  sea-urchin  eggs  and 
embryo,  the  chemical  processes  which  determine  natural 
death  are  certainly  not  identical  with  the  processes  which 
underlie  their  development.  T.  B.  Robertson  has  also  arrived 
at  the  conclusion,  for  quite  different  reasons,  that  the  process 
of  senile  decay  is  essentially  different  from  that  of  growth  and 
development. 

1  Weismann  showed  that  infusorians  or  unicellular  organisms  in  general  are 
immortal,  while  he  assumed  that  aU  the  other  organisms  with  the  exception  of  their 
germ-plasm  are  mortal.  Leo  Loeb  first  called  attention  to  the  fact  that  the 
transplantation  of  a  cancer  can  be  repeated  to  an  unlimited  series  of  generations, 
and  since  it  is  the  originally  transplanted  cancer-cell  and  the  cells  derived  from  it 
by  multiplication  that  survive,  he  pointed  out  that  this  proved  that  the  principle 
of  immortality  must  also  be  granted  to  cancer-cells  (1901).  Later  he  generalized 
this  idea  and  stated  that  other  cells  may  be  considered  immortal  ia  the  same 
sense  in  which  Weismann  claimed  this  for  the  imicellular  organisms.  One  can 
indeed  well  imagine  that  the  same  piece  of  skin  might  be  transplanted  through  an 
indefinite  series  of  generations  of  mice  and  that  such  a  transplanted  piece  might 
outlive  an  indefinite  nimiber  of  generations  of  mice  in  exactly  the  same  way  as  a 
cancer  cell  does. 

The  natural  death  of  the  metazoa  is  perhaps  a  secondary  phenomenon  due 
to  the  cessation  of  respiratory  motions  or  of  the  heart  beat.  This  leads  to  the 
death  of  the  cells  through  lack  of  oxygen.  If  respiratory  motions  and  circulation 
could  be  maintained  indefinitely  even  the  metazoa  might  be  foxmd  to  be  irmnortal. 


Influence  of  Environment  on  Animals       211 


6)  Changes  in  the  color  of  butterflies  produced  through  the 
influence  of  temperature. — The  experiments  of  Dorfmeister, 
Weismann,  Merrifield,  Standfuss,  and  Fischer  on  seasonal 
dimorphism  and  the  aberration  of  color  in  butterflies  have  so 
often  been  discussed  in  biological  literature  that  a  short  refer- 
ence to  them  will  suffice.  By  seasonal  dimorphism  is  meant 
the  fact  that  species  may  appear  at  different  seasons  of  the  year 
in  a  somewhat  different  form  or  color.  Vanessa  prorsa  is  the 
summer  form,  Vanessa  levana  the  winter  form  of  the  same 
species.  By  keeping  the  pupae  of  Vanessa  prorsa  several 
weeks  at  a  temperature  of  from  0°  to  1°  Weismann  succeeded 
in  obtaining  from  the  summer  chrysalids  specimens  which 
resembled  the  winter  variety,  Vanessa  levana. 

If  we  wish  to  get  a  clear  imderstanding  of  the  causes  of 
variation  in  the  color  and  pattern  of  butterflies,  we  must  direct 
our  attention  to  the  experiments  of  Fischer,  who  worked  with 
more  extreme  temperatures  than  his  predecessors,  and  found 
that  almost  identical  aberrations  of  color  could  be  produced 
by  both  extremely  high  and  extremely  low  temperatures.  This 
can  be  seen  clearly  from  the  following  tabulated  results  of  his 
observations.  At  the  head  of  each  column  the  temperature 
to  which  Fischer  submitted  the  pupae  is  given,  and  in  the 
vertical  column  below  are  found  the  varieties  that  were  pro- 
duced.    In  the  vertical  column  A  are  given  the  normal  forms : 


0°to-20°C. 

0°  to 
+  10°  C. 

A  (Normal 
Forms) 

+  35°  to 
+  37°  C. 

+  36°  to 
+  41°  C. 

+  42°  to 
+  46°  C. 

ichnusoides 

polaris 

urticae 

ichnusa 

polaris 

ichnusoides 

(nigrita) 
antigone 

fischeri 

io 

fischeri 

(nigrita) 
antigone 

(iokaste) 
testudo 

dixeyi 

poly- 
chloros 

erythrome- 
las 

dixeyi 

(iokaste) 
testudo 

hygiaea 
elymi 

artemis 
wiskotti 

antiopa 
cardui 

epione 

artemis 
wiskotti 

hygiaea 
ehoni 

klymene 

merri- 
fieldi 

atalanta 

merri- 
fieldi 

klymene 

weismanni 

porima 

prorsa 

porima 

weismanm 

212         The   Mechanistic  Conception  of  Life 

The  reader  will  notice  that  the  aberrations  produced  at  a 
very  low  temperature  (from  0°  to  —20°  C.)  are  absolutely 
identical  with  the  aberrations  produced  by  exposing  the  pupae 
to  extremely  high  temperatures  (from  42°  to  46°  C.)  •  Moreover 
the  aberrations  produced  by  a  moderately  low  temperature 
(from  0°  to  10°  C.)  are  dentical  with  the  aberrations  produced 
by  a  moderately  high  temperature  (from  36°  to  41°  C.)- 

From  these  observations  Fischer  concludes  that  it  is  errone- 
ous to  speak  of  a  specific  effect  of  high  and  of  low  temperatures, 
but  that  there  must  be  a  common  cause  for  the  aberration  found 
at  the  high  as  well  as  at  the  low  temperature  limits  „  This  cause 
he  seems  to  find  in  the  inhibiting  effects  of  extreme  temperatures 
upon  development. 

If  we  try  to  analyze  such  results  as  Fischer's  from  a  physico- 
chemical  point  of  view,  we  must  realize  that  what  we  call  life 
consists  of  a  series  of  chemical  reactions,  which  are  connected 
in  a  catenary  way;  inasmuch  as  one  reaction  or  group  of  reac- 
tions (a)  (e.g.,  hydrolyses)  causes  or  furnishes  the  material  for 
a  second  reaction  or  group  of  reactions,  (h)  (e.g.,  oxidations). 
We  know  that  the  temperature  coefficient  for  physiological 
processes  varies  slightly  at  various  parts  of  the  scale;  as  a  rule 
it  is  higher  near  0°  and  lower  near  30°.  But  we  know  also  that 
the  temperature  coefficients  do  not  vary  equally  for  the  various 
physiological  processes.  It  is,  therefore,  to  be  expected  that 
the  temperature  coefficients  for  the  group  of  reactions  of  the 
type  (a)  will  not  be  identical  through  the  whole  scale  with  the 
temperature  coefficients  for  the  reactions  of  the  type  (6).  If, 
therefore,  a  certain  substance  is  formed  at  the  normal  tempera- 
ture of  the  animal  in  such  quantities  as  are  needed  for  the 
catenary  reaction  (6),  it  is  not  to  be  expected  that  this  same 
perfect  balance  will  be  maintained  for  extremely  high  or 
extremely  low  temperatures;  it  is  more  probable  that  one  group 
of  reactions  will  exceed  the  other  and  thus  produce  aberrant 


Influence  of  Envieonment  on  Animals       213 

chemical   effects,   which  may  underlie   the   color   aberrations 
observed  by  Fischer  and  other  experimenters. 

It  is  important  to  notice  that  Fischer  was  also  able  to  produce 
aberrations  through  the  application  of  narcotics.  Wolfgang 
Ostwald  has  produced  experimentally,  through  variation  of 
temperature,  dimorphism  of  form  in  Daphnia. 

IV.      THE    EFFECTS    OF   LIGHT 

At  the  present  day  nobody  seriously  questions  the  statement 
that  the  action  of  light  upon  organisms  is  primarily  one  of  a 
chemical  character.  While  this  chemical  action  is  of  the 
utmost  importance  for  organisms,  the  nutrition  of  which 
depends  upon  the  action  of  chlorophyll,  it  becomes  of  less 
importance  for  organisms  devoid  of  chlorophyll.  Nevertheless, 
we  find  animals  in  which  the  formation  of  organs  by  regenera- 
tion is  not  possible  unless  they  are  exposed  to  light.  An 
observation  made  by  the  writer  on  the  regeneration  of  polyps 
in  a  hydroid,  Eudendrium  racemosum,  at  Woods  Hole,  may  be 
mentioned  as  an  instance  of  this.  If  the  stem  of  this  hydroid, 
which  is  usually  covered  with  polyps,  is  put  into  an  aquarium  the 
polyps  soon  fall  off.  If  the  stems  are  kept  in  an  aquarium 
where  light  strikes  them  during  the  day,  a  regeneration  of 
numerous  polyps  takes  place  in  a  few  days.  If,  however,  the 
stems  of  Eudendrium  are  kept  permanently  in  the  dark,  no 
polyps  are  formed  even  after  an  interval  of  some  weeks;  but 
they  are  formed  in  a  few  days  after  the  same  stems  have  been 
transferred  from  the  dark  to  the  light.  Diffused  daylight 
suffices  for  this  effect.  Goldfarb,  who  repeated  these  experi- 
ments, states  that  an  exposure  of  comparatively  short  duration 
is  sufficient  to  produce  this  effect.  It  is  possible  that  the  light 
favors  the  formation  of  substances  which  are  a  prerequisite 
for  the  origin  of  polyps  and  their  growth. 

Of  much  greater  significance  than  this  observation  are  the 


214         The  Mechanistic  Conception  of  Life 

facts  which  show  that  a  large  number  of  animals  assume,  to 
some  extent,  the  color  of  the  ground  on  which  they  are  placed. 
Pouchet  found  through  experiments  upon  crustaceans  and  fish 
that  this  influence  of  the  ground  on  the  color  of  animals  is 
produced  through  the  medium  of  the  eyes.  If  the  eyes  are 
removed  or  the  animals  made  blind  in  another  way  these 
phenomena  cease.  The  second  general  fact  found  by  Pouchet 
was  that  the  variation  in  the  color  of  the  animal  is  brought 
about  through  an  action  of  the  nerves  on  the  pigment  cells  of 
the  skin;  the  nerve  action  being  induced  through  the  agency 
of  the  eye. 

The  mechanism  and  the  conditions  for  the  change  in  colora- 
tion were  made  clear  through  the  beautiful  investigations  of 
Keeble  and  Gamble,  on  the  color  change  in  crustaceans. 
According  to  these  authors  the  pigment  cells  can,  as  a  rule,  be 
considered  as  consisting  of  a  central  body  from  which  a  system 
of  more  or  less  complicated  ramifications  or  processes  spreads 
out  in  all  directions.  As  a  rule,  the  center  of  the  cell  contains 
one  or  more  different  pigments  which  under  the  influence  of 
nerves  can  spread  out  separately  or  together  into  the  ramifica- 
tions. These  phenomena  of  spreading  and  retraction  of  the 
pigments  into  or  from  the  ramifications  of  the  pigment  cells 
form  on  the  whole  the  basis  for  the  color  changes  under  the 
influence  of  environment.  Thus  Keeble  and  Gamble  observed 
that  Macromysis  flexuosa  appears  transparent  and  colorless 
or  gray  on  sandy  ground.  On  a  dark  ground  their  color 
becomes  darker.  These  animals  have  two  pigments  in  their 
chromatophores,  a  brown  pigment  and  a  whitish  or  yellow 
pigment;  the  former  is  much  more  plentiful  than  the  latter. 
When  the  animal  appears  transparent  all  the  pigment  is  con- 
tained in  the  center  of  the  cells,  while  the  ramifications  are  free 
from  pigment.  When  the  animal  appears  brown  both  pigments 
are  spread  out  into  ramifications.  In  the  condition  of  maximal 
spreading  the  animals  appear  black. 


Influence  of  Environment  on  Animals       215 

This  is  a  comparatively  simple  case.  Much  more  compli- 
cated conditions  were  fomid  by  Keeble  and  Gamble  in  other 
crustaceans,  e.g.,  in  Hippolyte  cranchii,  but  the  influence  of  the 
surroundings  upon  the  coloration  of  this  form  was  also  satis- 
factorily analyzed  by  these  authors. 

While  many  animals  show  transitory  changes  in  color  under 
the  influence  of  their  surroundings,  in  a  few  cases  permanent 
changes  can  be  produced.  The  best  examples  of  this  are  those 
which  were  observed  by  Poulton  in  the  chrysalids  of  various 
butterflies,  especially  the  small  tortoise-shell.  These  experi- 
ments are  so  well  known  that  a  short  reference  to  them  will 
suffice.  Poulton^  found  that  in  gilt  or  white  surroundings  the 
pupae  became  light  colored  and  there  was  often  an  immense 
development  of  the  golden  spots,  ''so  that  in  many  cases  the 
whole  surface  of  the  pupae  glittered  with  an  apparent  metallic 
luster.  So  remarkable  was  the  appearance  that  a  physicist, 
to  whom  I  showed  the  chrysahds,  suggested  that  I  had  played  a 
trick  and  had  covered  them  with  goldleaf."  When  black  sur- 
roundings were  used,  ''the  pupae  were  as  a  rule  extremely  dark, 
with  only  the  smallest  trace,  and  often  no  trace  at  all,  of  the 
golden  spots  which  are  so  conspicuous  in  the  lighter  form." 
The  susceptibility  of  the  animal  to  this  influence  of  its  surround- 
ings was  found  to  be  greatest  during  a  definite  period  when  the 
caterpillar  undergoes  the  metamorphosis  into  the  chrysalis  stage. 
As  far  as  the  writer  is  aware,  no  physico-chemical  explanation, 
except  possibly  Wieners'  suggestion  of  color  photography  by 
mechanical  color  adaptation,  has  ever  been  offered  for  the 
results  of  the  type  of  those  observed  by  Poulton. 

V.    effects  of  gravitation 
a)  Experiments  on  the  egg  of  the  frog. — Gravitation  can  only 
indirectly  affect  life  phenomena;  namely,  when  we  have  in  a 
cell  two  different  non-miscible  liquids  (or  a  liquid  and  a  solid) 

1  Poulton,  E.  B.,  Colours  of  Animals  ("International  Scientific  Series"), 
London,  1890,  p.  121. 


216         The  Mechanistic  Conception  of  Life 

of  different  specific  gravity,  so  that  a  change  in  the  position  of 
the  cell  or  the  organ  may  give  results  which  can  be  traced  to  a 
change  in  the  position  of  the  two  substances.  This  is  very 
nicely  illustrated  by  the  frog's  egg,  which  has  two  layers  of  very 
viscous  protoplasm  one  of  which  is  black  and  one  white.  The 
dark  one  occupies  normally  the  upper  position  in  the  egg  and 
may  therefore  be  assumed  to  possess  a  smaller  specific  gravity 
than  the  white  substance.  When  the  egg  is  turned  with  the 
white  pole  upward  a  tendency  of  the  white  protoplasm  to  flow 
down  again  manifests  itself.  It  is,  however,  possible  to  prevent 
or  retard  this  rotation  of  the  highly  viscous  protoplasm,  by 
compressing  the  eggs  between  horizontal  glass  plates.  Such 
compression  experiments  may  lead  to  rather  interesting  results, 
as  O.  Schultze  first  pointed  out.  Pfliiger  had  already  shown 
that  the  first  plane  of  division  in  a  fertilized  frog's  egg  is  vertical 
and  Roux  established  the  fact  that  the  first  plane  of  division  is 
identical  with  the  plane  of  symmetry  of  the  later  embryo. 
Schultze  found  that  if  the  frog's  egg  is  turned  upside  down  at  the 
time  of  its  first  division  and  kept  in  this  abnormal  position, 
through  compression  between  two  glass  plates  for  about  twenty 
hours,  a  small  number  of  eggs  may  give  rise  to  twins.  It  is 
possible,  in  this  case,  that  the  tendency  of  the  black  part  of  the 
egg  to  rotate  upward  along  the  surface  of  the  egg  leads  to  a 
separation  of  its  first  cells,  such  a  separation  leading  to  the 
formation  of  twins. 

T.  H.  Morgan  made  an  interesting  additional  observation. 
He  destroyed  one-half  of  the  egg  after  the  first  segmentation 
and  found  that  the  half  which  remained  alive  gave  rise  to  only 
one-half  of  an  embryo,  thus  confirming  an  older  observation  of 
Roux.  When,  however,  Morgan  put  the  egg  upside  down  after 
the  destruction  of  one  of  the  first  two  cells,  and  compressed  the 
eggs  between  two  glass  plates,  the  surviving  half  of  the  egg  gave 
rise  to  a  perfect  embryo  of  half-size  (and  not  to  a  half-embryo 
of  normal  size  as  before) .     Obviously  in  this  case  the  tendency 


Influence  of  Environment  on  Animals       217 

of  the  protoplasm  to  flow  back  to  its  normal  position  was 
partially  successful  and  led  to  a  partial  or  complete  separation 
of  the  living  from  the  dead  half;  whereby  the  former  was 
enabled  to  form  a  whole  embryo,  which,  of  course,  possessed 
only  half  the  size  of  an  embryo  originating  from  a  whole  egg. 

h)  Experiments  on  hydroids. — A  striking  influence  of  gravita- 
tion can  be  observed  in  a  hydroid,  Antennularia  antennina, 
from  the  Bay  of  Naples.  This  hydroid  consists  of  a  long, 
straight,  main  stem  which  grows  vertically  upward  and 
which  has  at  regular  intervals  very  fine  and  short  bristle- 
like lateral  branches,  on  the  upper  side  of  which  the  polyps 
grow.  The  main  stem  is  negatively  geotropic,  i.e.,  its  apex 
continues  to  grow  vertically  upward  when  we  put  it  obliquely 
into  the  aquarium,  while  the  roots  grow  vertically  downward. 
The  writer  observed  that  when  the  stem  is  put  horizontally 
into  the  water  the  short  lateral  branches  on  the  lower  side 
give  rise  to  an  altogether  different  kind  of  organ,  namely,  to 
roots,  and  these  roots  grow  indefinitely  in  length  and  attach 
themselves  to  solid  bodies;  while  if  the  stem  had  remained  in  its 
normal  position  no  further  growth  would  have  occurred  in  the 
lateral  branches.  From  the  upper  side  of  the  horizontal  stem 
new  stems  grow  out,  mostly  directly  from  the  original  stem, 
occasionally  also  from  the  short  lateral  branches.  It  is  thus 
possible  to  force  upon  this  hydroid  an  arrangement  of  organs 
which  is  altogether  different  from  the  hereditary  arrangement. 
The  writer  had  called  the  change  in  the  hereditary  arrange- 
ment of  organs  or  the  transformation  of  organs  by  external 
forces  heteromorphosis.  We  cannot  now  go  any  farther  into 
this  subject,  which  should,  however,  prove  of  interest  in  rela- 
tion to  the  problem  of  heredity. 

If  it  is  correct  to  apply  inferences  drawn  from  the  observa- 
tion on  the  frog's  egg  to  the  behavior  oi  Antennularia,  one  might 
conclude  that  the  cells  of  Antennularia  also  contain  non-miscible 
substances   of   different   specific   gravity,  and  that  wherever 


218         The   Mechanistic  Conception  of  Life 

the  specifically  lighter  substance  comes  in  contact  with  the 
sea-water  (or  gets  near  the  surface  of  the  cell)  the  growth  of  a 
stem  is  favored ;  while  contact  with  the  sea-water  of  the 
specifically  heavier  of  the  substances,  will  favor  the  formation 
of  roots. 

VI.    the  experimental  control  of  animal  instincts 

a)  Experiments  on  the  mechanism  of  heliotropic  reactions  in 
animals. — Since  the  instinctive  reactions  of  animals  are  as 
hereditary  as  their  morphological  character,  a  discussion  of 
experiments  on  the  physico-chemical  character  of  the  instinctive 
reactions  of  animals  should  not  be  entirely  omitted  from  this 
sketch.  It  is  obvious  that  such  experiments  must  begin  with 
the  simplest  type  of  instincts,  if  they  are  expected  to  lead  to 
any  results;  and  it  is  also  obvious  that  only  such  animals  must 
be  selected  for  this  purpose,  the  reactions  of  which  are  not 
complicated  by  associative  memory  or,  as  it  may  preferably  be 
termed,  associative  hysteresis. 

The  simplest  type  of  instincts  is  represented  by  the  purpose- 
ful motions  of  animals  to  or  from  a  source  of  energy,  e.g.,  light; 
and  it  is  with  some  of  these  that  we  intend  to  deal  here.  When 
we  expose  winged  aphides  (after  they  have  flown  away  from  the 
plant),  or  young  caterpillars  of  Porthesia  chrysorrhoea  (when 
they  are  aroused  from  their  winter  sleep),  or  marine  or  fresh- 
water copepods  and  many  other  animals,  to  diffused  daylight 
falling  in  from  a  window,  we  notice  a  tendency  among  these 
animals  to  move  toward  the  source  of  light.  If  the  animals  are 
naturally  sensitive,  or  if  they  are  rendered  sensitive  through  the 
agencies  which  we  shall  mention  later,  and  if  the  fight  is  strong 
enough,  they  move  toward  the  source  of  fight  in  as  straight  a 
line  as  the  imperfections  and  pecufiarities  of  their  locomotor 
apparatus  wifi  permit.  It  is  also  obvious  that  we  are  here 
dealing  with  a  forced  reaction  in  which  the  animals  have  no 
more  choice  in  the  direction  of  their  motion  than  have  the  iron 


Influence  of  Environment  on  Animals       219 

filings  in  their  arrangement  in  a  magnetic  field.  This  can  be 
proved  very  nicely  in  the  case  of  starving  caterpillars  of  Por- 
thesia.  The  writer  put  such  caterpillars  into  a  glass  tube  the 
axis  of  which  was  at  right  angles  to  the  plane  of  the  window: 
the  caterpillars  went  to  the  window  side  of  the  tube  and 
remained  there,  even  if  leaves  of  their  food  plant  were  put  into 
the  tube  directly  behind  them.  Under  such  conditions  the 
animals  actually  died  from  starvation,  the  light  preventing 
them  from  turning  to  the  food,  which  they  eagerly  ate  when  the 
light  allowed  them  to  do  so.  One  cannot  say  that  these  animals, 
which  we  call  positively  heliotropic,  are  attracted  by  the  light, 
since  it  can  be  shown  that  they  go  toward  the  source  of  light 
even  if  in  so  doing  they  move  from  places  of  a  higher  to  places 
of  a  lower  degree  of  illumination. 

The  writer  has  advanced  the  following  theory  of  these 
instinctive  reactions.  Animals  of  the  type  of  those  mentioned 
are  automatically  oriented  by  the  light  in  such  a  way  that 
symmetrical  elements  of  their  retina  (or  skin)  are  struck  by 
the  rays  of  light  at  the  same  angle.  In  this  case  the  intensity 
of  light  is  the  same  for  both  retinae  or  symmetrical  parts  of  the 
skin. 

This  automatic  orientation  is  determined  by  two  factors, 
first  a  peculiar  photosensitiveness  of  the  retina  (or  skin),  and 
second  a  peculiar  nervous  connection  between  the  retina  and 
the  muscular  apparatus.  In  symmetrically  built  heliotropic 
animals  in  which  the  symmetrical  muscles  participate  equally 
in  locomotion,  the  symmetrical  muscles  work  with  equal  energj^ 
as  long  as  the  photochemical  processes  in  both  eyes  are  identi- 
cal. If,  however,  one  eye  is  struck  by  stronger  light  than  the 
other,  the  symmetrical  muscles  will  work  unequally  and  in 
positively  heliotropic  animals  those  muscles  will  work  with 
greater  energy  which  brings  the  plane  of  symmetry  back  into 
the  direction  of  the  rays  of  light  and  the  head  toward  the  source 
of  light.     As  soon  as  both  eyes  are  struck  by  the  rays  of  light 


220         The   Mechanistic  Conception  of  Life 

at  the  same  angle,  there  is  no  more  reason  for  the  animal  to 
deviate  from  this  direction  and  it  will  move  in  a  straight  line. 
All  this  holds  good  on  the  supposition  that  the  animals  are 
exposed  to  only  one  source  of  light  and  are  very  sensitive  to 
light. 

Additional  proof  for  the  correctness  of  this  theory  was 
furnished  through  the  experiments  of  G.  H.  Parker  and  S.  J. 
Holmes.  The  former  worked  on  a  butterfly,  Vanessa  antiope, 
the  latter  on  other  arthropods.  All  the  animals  were  in  a 
marked  degree  positively  heliotropic.  These  authors  found 
that  if  one  cornea  is  blackened  in  such  an  animal,  it  moves 
continually  in  a  circle  when  it  is  exposed  to  a  source  of  light, 
and  in  these  motions  the  eye  which  is  not  covered  with  paint  is 
directed  toward  the  center  of  the  circle.  The  animal  behaves, 
therefore,  as  if  the  darkened  eye  were  in  the  shade. 

h)  The  production  of  positive  heliotropism  hy  acids  and  other 
means  and  the  periodic  depth  migrations  of  pelagic  animals. — • 
When  we  observe  a  dense  mass  of  copepods  collected  from  a 
fresh-water  pond,  we  notice  that  some  have  a  tendency  to  go  to 
the  light  while  others  go  in  the  opposite  direction  and  many, 
if  not  the  majority,  are  indifferent  to  light.  It  is  an  easy  matter 
to  make  the  negatively  hehotropic  or  the  indifferent  copepods 
almost  instantly  positively  heliotropic  by  adding  a  small  but 
definite  amount  of  carbon  dioxide  in  the  form  of  carbonated 
water  to  the  water  in  which  the  animals  are  contained.  If  the 
animals  are  contained  in  50  c.c.  of  water  it  suffices  to  add  from 
3  to  6  c.c.  of  carbonated  water  to  make  all  the  copepods  energeti- 
cally positively  heliotropic.  This  heliotropism  lasts  about 
half  an  hour  (probably  until  all  the  carbon  dioxide  has  again 
diffused  into  the  air).  Similar  results  may  be  obtained  with 
any  other  acid. 

The  same  experiments  may  be  made  with  another  fresh- 
water crustacean,  namely  Daphnia,  with  this  difference,  how- 
ever, that  it  is  as  a  rule  necessary  to  lower  the  temperature  of 


Influence  of  Environment  on  Animals       221 

the  water  also.  If  the  water  containing  the  Daphniae  is  cooled 
and  at  the  same  time  carbon  dioxide  added,  the  animals  which 
were  before  indifferent  to  light  now  become  most  strikingly 
positively  heliotropic.  Marine  copepods  can  be  made  posi- 
tively heliotropic  by  the  lowering  of  the  temperature  alone,  or 
by  a  sudden  increase  in  the  concentration  of  the  sea-water. 

These  data  have  a  bearing  upon  the  depth  migrations  of 
pelagic  animals,  as  was  pointed  out  years  ago  by  Theo.  T.  Groom 
and  the  writer.  It  is  well  known  that  many  animals  living 
near  the  surface  of  the  ocean  or  fresh-water  lakes,  have  a 
tendency  to  migrate  upward  toward  evening  and  downward 
in  the  morning  and  during  the  day.  These  periodic  motions 
are  determined  to  a  large  extent,  if  not  exclusively,  by  the 
heliotropism  of  these  animals.  Since  the  consumption  of  carbon 
dioxide  by  the  green  plants  ceases  toward  evening,  the  tension 
of  this  gas  in  the  water  must  rise  and  this  must  have  the  effect 
of  inducing  positive  heliotropism  or  increasing  its  intensity. 
At  the  same  time  the  temperature  of  the  water  near  the  surface 
is  lowered  and  this  also  increases  the  positive  heliotropism  in  the 
organisms. 

The  faint  light  from  the  sky  is  sufficient  to  cause  animals 
which  are  in  a  high  degree  positively  heliotropic  to  move 
vertically  upward  toward  the  light,  as  experiments  with  such 
pelagic  animals,  e.g.,  copepods,  have  shown.  When,  in  the 
morning,  the  absorption  of  carbon  dioxide  by  the  green  algae 
begins  again  and  the  temperature  of  the  water  rises,  the  animals 
lose  their  positive  heliotropism,  and  slowly  sink  down  or  become 
negatively  heliotropic  and  migrate  actively  downward. 

These  experiments  have  also  a  bearing  upon  the  problem 
of  the  inheritance  of  instincts.  The  character  which  is  trans- 
mitted in  this  case  is  not  the  tendency  to  migrate  periodically 
upward  and  downward,  but  the  positive  heliotropism.  The' 
tendency  to  migrate  is  the  outcome  of  the  fact  that  periodically 
varying  external  conditions  induce  a  periodic  change  in  the 


222         The   Mechanistic  Conception  of  Life 

sense  and  intensity  of  the  heliotropism  of  these  animals.  It 
is  of  course  immaterial  for  the  result,  whether  the  carbon 
dioxide  or  any  other  acid  diffuse  into  the  animal  from  the  out- 
side or  whether  they  are  produced  inside  in  the  tissue-cells  of 
the  animals.  Davenport  and  Cannon  found  that  Daphniae, 
which  at  the  beginning  of  the  experiment  react  sluggishly  to 
light,  react  much  more  quickly  after  they  have  been  made  to 
go  to  the  light  a  few  times.  The  writer  is  inclined  to  attribute 
this  result  to  the  effect  of  acids,  e.g.,  carbon  dioxide,  produced 
in  the  animals  themselves  in  consequence  of  their  motion. 
A  similar  effect  of  the  acids  was  shown  by  A.  D.  Waller  in  the 
case  of  the  response  of  a  nerve  to  stimuli. 

The  writer  observed  many  years  ago  that  winged  male  and 
female  ants  are  positively  heliotropic  and  that  their  heliotropic 
sensitiveness  increases  and  reaches  its  maximum  toward  the 
period  of  nuptial  flight.  Since  the  workers  show  no  heliotropism 
it  looks  as  if  an  internal  secretion  from  the  sexual  glands  were 
the  cause  of  their  heUotropic  sensitiveness.  V.  Kellogg  has 
observed  that  bees  also  become  intensely  positively  heliotropic 
at  the  period  of  their  wedding  flight,  in  fact  so  much  so  that  by 
letting  light  fall  into  the  observation  hive  from  above,  the  bees 
are  prevented  from  leaving  the  hive  through  the  exit  at  the 
lower  end. 

We  notice  also  the  reverse  phenomenon,  namely,  that 
chemical  changes  produced  in  the  animal  destroy  its  heli- 
otropism. The  caterpillars  of  Porthesia  chrysorrhoea  are  very 
strongly  positively  heUotropic  when  they  are  first  aroused  from 
their  winter  sleep.  This  heliotropic  sensitiveness  lasts  only  as 
long  as  they  are  not  fed.  If  they  are  kept  permanently  without 
food  they  remain  permanently  positively  heliotropic  until 
they  die  from  starvation.  It  is  to  be  inferred  that  as  soon  as 
these  animals  take  up  food,  the  formation  of  a  substance  or 
substances  in  their  bodies  takes  place,  diminishing  or  annihilat- 
ing their  heliotropic  sensitiveness. 


Influence  of  Environment  on  Animals       223 

The  heliotropism  of  animals  is  identical  with  the  heli- 
otropism  of  plants.  The  writer  has  shown  that  the  experiments 
on  the  effect  of  acids  on  the  heliotropism  of  copepods  can  be 
repeated  with  the  same  result  in  Volvox.  It  is,  therefore, 
erroneous  to  try  to  explain  these  heliotropic  reactions  of  animals 
on  the  basis  of  peculiarities  (e.g.,  vision)  which  are  not  found 
in  plants. 

We  may  briefly  discuss  the  question  of  the  transmission 
through  the  sex-cells  of  such  instincts  as  are  based  upon  heli- 
otropism. This  problem  reduces  itself  simply  to  that  of  the 
method  whereby  the  gametes  transmit  heliotropism  to  the  larvae 
or  to  the  adult.  The  writer  has  expressed  the  idea  that  all 
that  is  necessary  for  this  transmission  is  the  presence  of  a  pho- 
tosensitive substance  in  the  eyes  (or  in  the  skin)  of  the  animal. 
For  the  transmission  of  this  the  gametes  need  not  contain 
anything  more  than  a  catalyzer  or  ferment  for  the  synthesis 
of  the  photosensitive  substance  in  the  body  of  the  animal. 
What  has  been  said  in  regard  to  animal  heliotropism  might, 
if  space  permitted,  be  extended,  mutatis  mutandis,  to  geotropism 
and  stereotropism. 

c)  The  tropic  reactions  of  certain  tissue-cells  and  the 
morphogenetic  effects  of  these  reactions. — Since  plant-cells  show 
heliotropic  reactions  identical  with  those  of  animals,  it  is  not 
surprising  that  certain  tissue-cells  also  show  reactions  which 
belong  to  the  class  of  tropisms.  These  reactions  of  tissue-cells 
are  of  special  interest  by  reason  of  their  bearing  upon  the 
inheritance  of  morphological  characters.  An  example  of  this 
is  found  in  the  tiger-like  marking  of  the  yolk  sac  of  the  embryo 
of  Fundulus  and  in  the  marking  of  the  young  fish  itself.  The 
writer  found  that  the  former  is  entirely,  and  the  latter  at  least 
in  part,  due  to  the  creeping  of  the  chromatophores  upon 
the  blood-vessels.  The  chromatophores  are  at  first  scattered 
irregularly  over  the  yolk  sac  and  show  their  characteristic 
ramifications  (Fig.  36,  p.  106).     There  is  at  that  time  no  definite 


224         The   Mechanistic  Conception  of  Life 

relation  between  blood-vessels  and  chromatophores.  As  soon 
as  a  ramification  of  a  chromatophore  comes  in  contact  with 
a  blood-vessel  the  whole  mass  of  the  chromatophore  creeps 
gradually  on  the  blood-vessel  (Fig.  37)  and  forms  a  complete 
sheath  around  the  vessel,  until  finally  all  the  chromatophores 
form  a  sheath  around  the  vessels  and  no  more  pigment  cells 
are  found  in  the  meshes  between  the  vessels  (Fig.  38).  Nobody 
who  has  not  actually  watched  the  process  of  the  creeping  of 
the  chromatophores  upon  the  blood-vessels  would  anticipate 
that  the  tiger-like  coloration  of  the  yolk  sac  in  the  later 
stages  of  development  was  brought  about  in  this  way.  Similar 
facts  can  be  observed  in  regard  to  the  first  marking  of 
the  embryo  itself.  The  writer  is  inclined  to  believe  that  we 
are  here  dealing  with  a  case  of  chemotropism,  and  that  the 
oxygen  of  the  blood  may  be  the  cause  of  the  spreading  of  the 
chromatophores  around  the  blood-vessels.  Certain  observa- 
tions seem  to  indicate  the  possibility  that  in  the  adult  the 
chromatophores  have,  in  some  forms  at  least,  a  more  rigid 
structure  and  are  prevented  from  acting  in  the  way  indicated. 
It  seems  to  the  writer  that  such  observations  as  those  made  on 
Fundulus  might  simplify  the  problem  of  the  hereditary  trans- 
mission of  certain  markings. 

Driesch  has  found  that  a  tropism  underlies  the  arrangement 
of  the  skeleton  in  the  pluteus  larvae  of  the  sea-urchin.  The 
position  of  this  skeleton  is  predetermined  by  the  arrangement 
of  the  mesenchyme  cells,  and  Driesch  has  shown  that  these 
cells  migrate  actively  to  the  place  of  their  destination,  possibly 
led  there  under  the  influence  of  certain  chemical  substances. 
When  Driesch  scattered  these  cells  mechanically  before  their 
migration,  they  nevertheless  reached  their  destination. 

In  the  developing  eggs  of  insects  the  nuclei,  together  with 
some  cytoplasm,  migrate  to  the  periphery  of  the  egg.  Herbst 
pointed  out  that  this  might  be  a  case  of  chemotropism,  caused 
by  the  oxygen  surrounding  the  egg.     The  writer  has  expressed 


Influence  of  Environment  on  Animals       225 

the  opinion  that  the  formation  of  the  blastula  may  be  caused 
generally  by  a  tropic  reaction  of  the  blastomeres,  the  latter 
being  forced  by  an  outside  influence  to  creep  to  the  surface  of 
the  egg. 

These  examples  may  suffice  to  indicate  that  the  arrangement 
of  definite  groups  of  cells  and  the  morphological  effects  resulting 
therefrom  may  be  determined  by  forces  lying  outside  the  cells. 
Since  these  forces  are  ubiquitous  and  constant  it  appears  as  if 
we  were  dealing  exclusively  with  the  influence  of  a  gamete; 
while  in  reality  all  that  is  necessary  for  the  gamete  to  transmit 
is  a  certain  form  of  irritability. 

d)  Factors  which  determine  place  and  time  for  the  deposition 
of  eggs. — For  the  preservation  of  species  the  instinct  of  animals 
to  lay  their  eggs  in  places  in  which  the  young  larvae  find  their 
food  and  can  develop  is  of  paramount  importance.  A  simple 
example  of  this  instinct  is  the  fact  that  the  common  fly  lays 
its  eggs  on  putrid  material  which  serves  as  food  for  the  young 
larvae.  When  a  piece  of  meat  and  of  fat  of  the  same  animal  are 
placed  side  by  side,  the  fly  will  deposit  its  eggs  upon  the  meat 
on  which  the  larvae  can  grow,  and  not  upon  the  fat,  on  which 
they  would  starve.  Here  we  are  dealing  with  the  effect  of  a 
volatile  nitrogenous  substance  which  reflexly  causes  the  peri- 
staltic motions  for  the  laying  of  the  egg  in  the  female  fly. 

Kammerer  has  investigated  the  conditions  for  the  laying  of 
eggs  in  two  forms  of  salamanders,  e.g.,  Salamandra  atra  and 
S.  maculosa.  In  both  forms  the  eggs  are  fertilized  in  the  body 
and  begin  to  develop  in  the  uterus.  Since  there  is  room  only 
for  a  few  larvae  in  the  uterus,  a  large  number  of  eggs  perish 
and  this  number  is  the  greater  the  longer  the  period  of  gestation. 
It  thus  happens  that  when  the  animals  retain  their  eggs  a  long 
time,  very  few  young  ones  are  born;  and  these  are  in  a  rather 
advanced  stage  of  development,  owing  to  the  long  time  which 
elapsed  since  they  were  fertilized.  When  the  animal  lays  its  eggs 
comparatively  soon  after  copulation,  many  eggs  (from  twelve  to 


226         The   Mechanistic  Conception  of  Life 

seventy-two)  are  produced  and  the  larvae  are  of  course  in  an 
early  stage  of  development.  In  the  early  stage  the  larvae  possess 
gills  and  can  therefore  live  in  water,  while  in  later  stages  they 
have  no  gills  and  breathe  through  their  lungs.  Kammerer 
showed  that  both  forms  of  Salamandra  can  be  induced  to  lay 
their  eggs  early  or  late,  according  to  the  physical  conditions 
surrounding  them.  If  they  are  kept  in  water  or  in  proximity 
to  water  and  in  a  moist  atmosphere  they  have  a  tendency  to 
lay  their  eggs  earlier  and  a  comparatively  high  temperature 
enhances  the  tendency  to  shorten  the  period  of  gestation.  If 
the  salamanders  are  kept  in  comparative  dryness  they  show  a 
tendency  to  lay  their  eggs  rather  late  and  a  low  temperature 
enhances  this  tendency. 

Since  Salamandra  atra  is  found  in  rather  dry  alpine  regions 
with  a  relatively  low  temperature  and  Salamandra  maculosa  in 
lower  regions  with  plenty  of  water  and  a  higher  temperature, 
the  fact  that  S.  atra  bears  young  which  are  already  developed 
and  beyond  the  stage  of  aquatic  life,  while  S.  maculosa  bears 
young  ones  in  an  earlier  stage,  has  been  termed  adaptation. 
Kammerer's  experiments,  however,  show  that  we  are  dealing 
with  the  direct  effects  of  definite  outside  forces.  While  we 
may  speak  of  adaptation  when  all  or  some  of  the  variables 
which  determine  a  reaction  are  unknown,  it  is  obviously  in  the 
interest  of  further  scientific  progress  to  connect  cause  and 
effect  directly  whenever  our  knowledge  allows  us  to  do  so. 

VII.     CONCLUDING   REMARKS 

The  discovery  of  DeVries,  that  new  species  may  arise  by 
mutation  and  the  wide  if  not  universal  applicability  of  Mendel's 
law  to  phenomena  of  heredity,  as  shown  especially  by  Bateson 
and  his  pupils,  must,  for  the  time  being,  if  not  permanently, 
serve  as  a  basis  for  theories  of  evolution.  These  discoveries 
place  before  the  experimental  biologist  the  definite  task  of  pro- 
ducing mutations  by  physico-chemical  means.     It  is  true  that 


Influence  of  Environment  on  Animals       227 

certain  authors  claim  to  have  succeeded  in  this,  but  the  writer 
wishes  to  apologize  to  these  authors  for  his  inability  to  convince 
himself  of  the  validity  of  their  claims  at  the  present  moment. 
He  thinks  that  only  continued  breeding  of  these  apparent 
mutants  through  several  generations  can  afford  convincing 
evidence  that  we  are  here  dealing  with  mutants  rather  than 
with  merely  pathological  variations.^ 

What  was  said  in  regard  to  the  production  of  new  species  by 
physico-chemical  means  may  be  repeated  with  still  more 
justification  in  regard  to  the  second  problem  of  transformation, 
namely,  the  making  of  living  from  inanimate  matter.  The 
purely  morphological  imitations  of  bacteria  or  cells  which 
physicists  have  now  and  then  proclaimed  as  artificially  produced 
living  beings,  or  the  plays  on  words  by  which,  e.g.,  the  regenera- 
tion of  broken  crystals  and  the  regeneration  of  lost  limbs  by 
a  crustacean  were  declared  identical  will  not  appeal  to  the 
biologist.  We  know  that  growth  and  development  in  animals 
and  plants  are  determined  by  definite  although  complicated 
series  of  catenary  chemical  reactions,  which  result  in  the  S3ai thesis 
of  a  definite  compound  or  group  of  compounds,  namely,  nucleins. 

The  nucleins  have  the  peculiarity  of  acting  as  ferments  or 
enzymes  for  their  own  synthesis.  Thus  a  given  type  of  nucleus 
will  continue  to  synthesize  other  nuclein  of  its  own  kind.  This 
determines  the  continuity  of  a  species;  since  each  species  has, 
probably,  its  own  specific  nuclein  or  nuclear  material.  But  it 
also  shows  us  that  whoever  claims  to  have  succeeded  in  making 
living  matter  from  inanimate  will  have  to  prove  that  he  has 
succeeded  in  producing  nuclear  material  which  acts  as  a  ferment 
for  its  own  synthesis  and  thus  reproduces  itself.  Nobody  has 
thus  far  succeeded  in  this,  although  nothing  warrants  us  in  taking 
it  for  granted  that  this  task  is  beyond  the  power  of  science. 

1  Since  this  was  written  the  beautiful  experiments  of  Kam merer  as  weU  as 
those  of  Tower  seem  to  have  furnished  proof  that  external  conditions  can  cause 
hereditary  changes  ia  animals. 


INDEX 


Abraxas,  17. 

Acid  poisoning,  18  flf. 

Acids,  influences  of,   on  heliotropism, 

42,  220;  acids  and  salts,  antagonism, 

of,  179  fl. 
Action  of  potassium  cyanide,  156  S. 
Activation  of  the  egg,  6  flf. 
Agalma,  208. 
Amphitrite,  144. 
Animal  instincts,  experimental  control 

of,  218. 
Antagonism  of  acids  and  salts,  179  flf. 
Antagonism  of  three  salts,  182  flf. 
Antagonistic  salt  action,  172  flf. 
Antedon  rosacea,  198. 
Antennularia    antennina,    85,    91,    107, 

217. 
Ants,  47,  48. 

Aphides,  19,  37  flf.,  41  flf.,  46. 
Arabacia,  157,  164,  190. 
Area  striata,  79. 
Arrhenius,  5,  198. 

Artificial  causation  of  positive  heliotro- 
pism, 43,  220. 
Artificial    parthenogenesis,     7,  116  flf., 

127  flf.,  199  flf. 
Artificial    production    of    double    and 

multiple  monstrosities  in  sea-urchins, 

100  flf. 
Artificial  production  of  living  matter,  5. 
Ascidians,  68. 

Associative  memory,  55,  73. 
Asterias  capitata,  198. 
Asterias  forbesii,  135. 
Asterias  ochracea,  138,  162,  198. 
Asterina,  132,  198. 
Atwater,  4. 
"Aura  seminalis,"  113. 

Baer,  K.  E.  von,  114. 
Balanus  perforatus,  46,  53. 
Baltzer,  15. 
Bancroft,  51. 
Bardeen,  92. 
Barry,  114. 

Bases      as      membrane-forming      sub- 
stances, 134. 
Bataillon,  11. 
Bateson,  226. 
Bees,  49. 

Beginning  of  scientific  biology,  4. 
Berzelius,  4. 
Biedermann,  173. 
Biology,  beginning  of  scientific,  4. 
Bischof,  115. 
Blaauw,  29. 
Bohn,  40,  49,  54,  55. 
Bolina,  208. 
Boveri,  15. 

Biitschli,  145,  146,  147. 
Bimsen,  27,  29,  30,  41,  58. 
Bimsen-Roscoe  law,  27,  28  flf.,  40,  58. 
Butyric  acid,  treatment  of  egg,  10. 


Callianira,  208. 

Cannon,  222. 

Catalysis  of  esters,  43. 

Catalyzer,  4,  5. 

"Center  of  coordination,"  72. 

Cerianthus  membranaceus,  93. 

Chaetopterus,  117. 

Change  in  intensity  of  light,  54  ff. 

Changes  in  color  of  butterflies  pro- 
duced through  influence  of  tempera- 
tm-e,  211. 

Chemical  agencies,  eflfects  of,  196  flf. 

Chemical  symmetry,  38,  39.    . 

Chemotropism,  224. 

Chlorostoma,  198. 

Chromosomes,  16  flf. 

Chim,  208. 

Ciamician,  38. 

Cinerarias,  37. 

Ciona  intestinalis,  68,  92. 

Claparede,  51. 

Cohen,  208. 

Color,  changes  in,  of  butterflies, 
through  influence  of  temperatiire, 
211;  color  adaptation,  80  flf.,  213  flf.; 
color  blindness,  16. 

Compulsory  movements,  38. 

Consciousness,  72. 

Contents  of  life,  26  flf. 

Cooke,  99. 

Cooperative  action  of  salts  causing 
impermeability  of  the  egg  mem- 
brane, 176  flf. 

Coordinated  movements  in  reflexes, 
70. 

Copepod,  43,  62. 

Correns,  21. 

Cortical  layer,  of  imfertilized  egg,  10, 
189;  mechanical  destruction  of, 
10,  11. 

Cosine  law  of  illumination,  41. 

Crabs,  fiddler,  60. 

Ctenolabrus,  25. 

Cuma  Rathkii,  51. 

Cytolysis,  of  the  egg,  146;  mechanical 
causation  of,  145. 

Cytolytic  agents,  10,  132  flf.,  136, 
144  flf.,  202. 

De  Vries,  226. 

Daphnia,  43,  208,  213,  220. 

Darwin,  Charles,  195,  196. 

Darwin,  F.,  58. 

Davenport,  222. 

Death     and     development,     different 

chemical   processes,    209  fl. 
Delage,  11,  131,  203. 
Depth  migration,  220. 
Development,     death     and,     diflferent 

chemical  processes,  209  flf. 
Diflference     of    salt    permeability     of 

various  membranes,  189  flf. 
Diflfusion  of  salts,  177  flf. 


229 


230 


The   Mechanistic   Conception  of  Life 


Doncaster,  21. 

Dorfmeister,  211. 

Driesch,  101,  108,  204,  224. 

Drosophila,  21. 

Dumas,  114. 

Dzierzon,  116. 

Ear,  otoliths  of,  and  orientation  to 
center  of  gravity  of  the  earth,  57. 

Effect  of  retarded  oxidations  on 
poisonous  salt  action,  190  fl. 

Effects  of  chemical  agencies,  196  fl.; 
of  gravitation,  215;    of  light,  213. 

Egg,  activation  of,  6  ff. ;  butyric  acid, 
treatment  of,  10;  cortical  layer  of 
tmfertilized,  10,  189;  increased 
sensitiveness  of  unfertilized,  to 
cytolytic  agents,  163  ff.;  produc- 
tion of  twins  from,  204  ff. 

Eggs,  factors  which  determine  time 
and  place  for  the  deposition  of,  225; 
immimity  of,  to  body  extracts  of 
same  species,  142;  varying  sus- 
ceptibility of,  144. 

Emidsion  theory  of  membrane  forma- 
tion, 145,  147  ff. 

Enzymes,  5,  122,  123. 

Esters,  catalysis  of,  43. 

Ethics,  3,  5,  31  ff.,  62. 

Eudendrium  racemosum,  213. 

Experimental  control  of  animal 
instincts,  218. 

Experiments,  on  hydroids,  217;  on 
the  egg  of  the  frog,  216;  on  the 
mechanism  of  heliotropic  reactions, 
218;    localization,  35. 

Factors  which  determine  time  and 
place  for  the  deposition  of  eggs, 
225. 

Ferments  of  oxidation,  5. 

Fertilization,  6;  fertilization  mem- 
brane, 8,  148  ff. 

Fiddler  crabs,  60. 

Fischer,  211,  212,  213. 

Fischer,  Emil,  115. 

Fovea  centralis,  39. 

France,  58. 

Froschl,  29. 

Fundulus  heteroclitus,  25,  105,  172  ff., 
175,  179  ff.,  223. 

Fusion  of  normally  double  organs,  207. 

Galvanotropism,  50  ff . 

Gamble,  214,  215. 

Gammarus,      170  ff.,      189;       poisonous 

action  of  distiUed  water  on,  170  ff. 
Gemmill,  121. 

Geotropism,  56  ff.,  89,  217,  223. 
Gies,  175. 

Godlewski,  15,  95,  198,  199. 
Goldfarb,  213. 
Gravitation,  effects  of,  215. 
Groom,  221.  , 

Growth,  96  ff.,  100 ff.;  mechanics  of,  in 

animals,  95. 
Growth  and  light,  213. 
Guyer,  17,  18. 

Haberlandt,  58. 
Hagedoorn,  15,  199. 
Handovski,  99. 
Hardy,  148. 


Harmonious  character  of  organisms, 
23  ff. 

Hartmann,  E.  von,  35. 

Harvey,  189. 

Heliotropic  animals,  41;  heliotropic 
reactions,  experiments  on  the  mech- 
anism of,  218. 

Heliotropism,  27  ff.,  220  ff.;  artificial 
causation  of  positive,  43,  220;  influ- 
ence of  acids  on,  42,  220. 

Henking,  16. 

Herbst,  92,  134,  186,  187,  204,  207,  224. 

Heredity,  4,  15  ff.,  49,  52,  101. 

Hertwig,  O.,  116,  134,  208. 

Hertwig,  R.,  7. 

Heterogeneous  hybridization,  24,  25, 
196  ff. 

Heteromorphosis,  85  ff.,  217  fl. 

Hippolyte  cranchii,  215. 

His,  100,  101,  115. 

Hoeber,  177. 

Holmes,  51,  60. 

Holmes,  S.  J.,  220. 

Huxley,  15. 

Huyghens,  104,  107. 

Hybridization,  heterogeneous,  24,  25, 
196  ff. 

Hybrids,  maternal  character  of  hetero- 
geneous, 199. 

Hydra,  93  ff . 

Hydroids,  Experiments  on,  217. 

Hypertonic  sea-water,  7,  116  ff.,  131  fl. 

Hypotricha,  55. 

Illumination,  Cosine  law  of,  41 ;  inten- 
sity of,  44. 

Imnumity,  142. 

Immunity  of  eggs  to  body  extracts 
of  same  species,  142. 

Increased  sensitiveness  of  unfertilized 
egg  to  cytolytic  agents,  163  fl. 

Influence  of  membrane  formation  in 
causing  the  egg  to  develop,  150  fl. 

Influence  of  temper atixre,  207  fl. 

Infusoria  Coelenterates,  74. 

Instincts,  69. 

Intensity  of  illumination,  44. 

Jacobi,  113. 
Jennings,  55,  60. 

Kammerer,  225,  226,  227. 

Keeble,  214,  215. 

KeUogg,  v.,  49,  222. 

Knaffl,  von,  136,  147. 

Koeppe,  148. 

Kupelwieser,  15,  21,  125,  198,  199. 

Laplace,  4,  5. 

Lavoisier,  4,  5. 

Law  of  segregation,  16,  20  fl. 

Leeuwenhook,  113. 

Liebig,  115. 

Life,  contents  of,  26  fl. 

"Life  principle,"  14,  15. 

Light,  change  in  intensity  of,  54  fl. 
effects  of,  213;  growth  and,  213 
photochemical  action  of,  30,  36 
selection  of  intensity  of,  by  animals 
52  ff. 

LiUie,  F.,  12. 

Lillie,  R.,  10,  132,  136,  174,  181. 


Index 


231 


Living    matter,    artificial    production 

of,  5. 
Localization  experiments,  35. 
Loeb,  Leo,  48,  210. 
Lottia,  209. 
Lucas,  208. 
Luther,  38. 
Lyon,  57. 

"Ly sin  theory,"  143. 
Lysins,  139  fl. 

McClung,  16,  17. 

Mach,  57. 

Macromysis  flexuosa,  214. 

Margelis,  89,  107. 

Maternal  character  of  heterogeneous 
hybrids,  199. 

Mathews,  A.  P.,  11,  144,  156. 

Maxwell,  S.  S.,  39,  208. 

Mead,  7,  117. 

Mechanical  causation  of  cytolysis,  145. 

Mechanical  destruction  of  cortical 
layer,  10,  11. 

Mechanics  of  growth  in  animals,  95. 

Membrane  of  fertilization,  8,  148  flf.; 
membrane-forming  substances,  bases 
as,  134;  membrane  formation,  emul- 
sion theory  of,  145, 147  S. ;  membrane 
formation,  influence  of,  in  causing  egg 
to  develop,  150  flf. 

Memory,  associative,  55,  73. 

Mendel,  4,  16,  20,  21,  49,  52,  59,  60, 
226. 

Mendel's  laws,  4,  15  flf.,  20,  49,  52, 
59  flf.,  226. 

Menidia,  25. 

Merrifleld,  211. 

Meyerhof,  190. 

Miescher,  114,  115. 

Minkowski,  79. 

Moenkhaus,  24. 

Monstrosities,  artificial  production  of, 
in  sea-urchins,  100  flf. 

Montgomery,  16. 

Morgan,  7,  17,  19,  21,  92,  117,  119,  216. 

Morphology,  physiological,  109. 

Movements,  compulsory,  38. 

Mimk,  35,  79. 

Muscles,  osmotic  phenomena  in,  99. 

Mytilus,  198. 

Natural  selection,  50  flf. 
Nemec,  58. 
Nereis,  12. 
Neuberg,  C,  38.    ' 
Norman,  117. 

Organisms,  harmonious  character  of, 
23  flf. 

Organs,  fusion  of  normally  double,  207. 

Osmotic  phenomena  in  muscles,  99. 

Osterhout,  177,  178,  179,  188. 

Ostwald,  Wilhelm,  4. 

Ostwald,  Wolfgang,  38,  213. 

Otoliths  of  ear  and  orientation  to 
center  of  gravity  of  the  earth,  57. 

Overton,  148,  177,  178,  179,  191. 

Oxidation,  ferments  of,  5. 

Oxidations,  and  their  relation  to  the 
egg  after  fertilization,  13, 157, 160  flf., 
164;  in  their  relation  to  life  and 
death,  14,  15;  eflfect  of  retarded,  on 
poisonous  salt  action,  190  flf. 


Parker,  39,  49,  220. 

Parthenogenesis,    117  flf.;    artificial,   7. 

116  flf.,  127  flf.,  199  flf. 
Parthenogenetic  development,  varying 

susceptibility  of  eggs  to,  144. 
PavOi,  99,  181. 
Pawlow,  62. 
Pennaria,  91. 
Peter,  208. 
Pettenkofer,  4. 
Pfliiger,  216. 

Photochemical  action  of  light,  30,  36. 
Photochemical,    eflfects,    27,    38,    39; 

substances,  39. 
Photosensitive  surfaces,  39. 
Photosensitiveness,  varying,  in  animals, 

45. 
Phylloxera,  19. 

Physiological  morphology,  109. 
Planarians,  39,  54. 
Plasmolysis,  177. 

Poisoning,  acid,   18  flf. ;    salt,   186  flf. 
Poisonous  action  of  distilled  water  on 

Gammarus,  170  flf. 
Polarization,  92  flf. 
Polygordius,  53. 
Polynoe,  132,  158. 
Porthesia   chrysorrhoea,  47,   48,   218  flf., 

222. 
Potassium  cyanide,  action  of,  156  flf. 
Pouchet,  80,  214. 
Poulton,  215. 
Prevost,  114. 
Procter,  181. 
Production    of    twins    from    one    egg 

through   a  change  in  the  chemical 

constitution  of  the  sea-water,  204  flf. 
Protective  solution,  172. 
Purposeful  character  of  refiexes,  66. 
Pycnopodia,  198. 
Pyrrhocoris,  16. 

Radl,  49. 

Ranke,  99. 

Rayleigh,  147,  152. 

Reflex,  65  flf. 

Reflexes,    coordinated   movements   in, 

70;   purposeful  character  of,  66. 
Reinke,  24. 
"Riddle  of  life,"  5. 
Ringer,  172,  173. 

Robertson,   T.   B.,   185,  208,   210. 
Role  of  water  in  segmentation,  99. 
Roscoe,  27,  29,  30,  41,  58. 
Roux,  24,  216. 
Rubner,  4. 

Sachs,  104.  107. 

Salamandra  atra,  225. 

Salamandra  maculosa,  225. 

Salt   poisoning,    186  flf. ;     diflference   of 

permeability  of  various  membranes, 

189  flf. 
Salts,  antagonism  of  acids  and,  179  flf.; 

antagonism    of    three    salts.    182  flf.; 

cooperative   action   of,    causing   im- 

permeabilitj^     of     egg     membrane, 

176  flf.;   diflfusion  of,  177  flf. 
Schmiedeberg,  173. 
Schopenhauer,  35. 
Schultze.  216. 

Sea-water,  hypertonic,  7,  116  flf.,  131  flf. 
Segregation,  law  of,  16,  20  flf. 


232 


The   Mechanistic  Conception  of  Life 


Selection,  of  intensity  of  light  by  ani- 
mals, 52  fl. ;    natural,  50  fl. 

Sex  determination,  16. 

Shearer,  11. 

Sipunculides,  141. 

Snyder,  C.  D.,  39,  208. 

Solution,  protective,  172. 

SpaUanzani,  113. 

Spermatozoa,  113  flf. 

Spermatozoon,  twofold  action  of,  in 
fertilization,   12  flf.,   132  flf.,   161  flf. 

"Speziflsche  Bildungsstoflfe,"  104. 

Spontaneous  movements,  71. 

Spyrogyra,  177  flf.,  188. 

Standfuss,  211. 

Stereotropism,  91  flf.,  223. 

Stevens,  17. 

Stieglitz,  43. 

Stockard,  206,  207. 

Strongylocentrotus  franciscanus,  140, 
198. 

Strongylocentrotus  purpuratus,  8,  139  flf., 
144,  162,  189,  197,  201,  205. 

Sumner,  80. 

Symmetry,  chemical,  38,  39. 

Temperature    as    a    cytolytic    agent, 

135flf.,  138  flf. 
Tower,  90,  227. 
Traube,  96. 
Tropisms,    26,    36  flf.,    54,    55,    60,    62, 

69,  70,  72. 
Tubularia  mesembryanthemum,  95,  97. 
Tunicates,  92. 
Twin  formation,  19,  205. 
Twins,  production  of,  from  egg,  204  flf. 
Twofold    action    of    spermatozoon    in 

fertilization,   12  flf.,   132  flf.,   161  flf. 


Tyrosin,  23. 

UexkueU,  70. 
"Unterschiedsempflndlichkeit,"  54. 

Van  Duyne,  92. 

van't  Hoflf,  208. 

Vanessa  antiope,  220. 

Vanessa  levana,  211. 

Vanessa  prorsa,  211. 

Varying  photosensitiveness  in  animals, 

45. 
Varying     susceptibility     of     eggs     of 

diflferent  species  to  parthenogenetic 

development,  144. 
Vaucheria,  188. 
Virchow,  127,  128. 
Vision,  79  flf. 
Voit,  4. 
Volvox,  51,  223. 

WaUer,  A.  D.,  222. 

Warburg,  13,  157,  160,  189,  190. 

Wasteneys,  13,  157,  181,  182. 

Water,   distilled,   poisonous   action   of 

distilled  water  on,   170  flf. ;    role  of, 

in  segmentation,  99. 
Weismann,  91,  210,  211. 
Wiener,  215. 
"Wm,"  35  flf.,  40. 
Wilson,  17,  18,  19. 

X-chromosomes,  18  flf. 

"Zielstrebigkeit,"  24. 
Zuntz,  4. 


DATE  DUE 

JAN  2 

l20Qb 

201-5503 

PRINTED  IN  U.S.A. 

J 


317102 


BOSTON  COLLEGE 


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